Blood, at least the blood we know about, has four main components: plasma, red blood cells, white blood cells, and platelets. Blood has many different functions, including: transporting oxygen and nutrients to the lungs and tissues, regulating body temperature, protect against disease by the use of white blood cells, protect against blood loss through clotting plus many other functions. The fact that we can’t live without it has been proven from the time William Harvey performed the first blood transfusion in 1665. However, not everyone, or everything, has the same blood or even the same blood components. Even in real life. One way to know is… what color does it bleed?
Blood is thicker—In the movies
Black Blood
Flash Gordon 1980 (General Kala) (Ming’s Dragon Klytus)
Blue Blood
The Fifth Element 1997 (Diva Plavalaguna)
Flash Gordon 1980 (prince)
Hellboy 2004 (Abe Sapien)
John Carter 2012 (Martians)
Men in Black 1997 (Mikey)
Pacific Rim 2013 (Kaiju)
Pitch Black 2000 (flying monsters) (bluish/gray)
Stardust 2007 (prince)
The World’s End 2013 (alien robots)
Green Blood
Castle of the Walking Dead 1967 (Anatol)
Demon Knight 1995 (The Collector and his Minions)
The Devil’s Rain 1975 (possessed worshipers) (sometimes brown)
Flash Gordon 1980 (Ming the Merciless)
Gamera 1965 (Gamera)
The Great Wall 2016 (Tao Tie)
The Green Slime 1968 (Slime creatures)
Leprechaun 4 1996 (alien princess)
Mad Doctor of Blood Island 1969 (Zombies)
Men in Black 1997 (Jack Jeebs)
Outlander 2008(Moorwen)
Predator 1987 (Predator) (florescent green/yellow)
Yamato Takeru 1994(Yamata no Orochi)
Orange Blood
Tremors 1990 (Graboids) (orangish/red)
Pink Blood
Gamera 1965 (Gyaos)
Star Trek VI: The Undiscovered Country 1991 (Klingon)
Purple Blood
Alice in Wonderland (2010) (Jabberwocky)
Gamera vs Barugon 1966 (Barugon)
White, Milky or Clear Blood
Alien 1979 (Androids)
Yellow Blood
Alien 1979 (Xenomorphs)
Hellboy II: The Golden Army 2008 (elven royalty) (yellow/gray)
Phantasm 1979 (The Tall Man)
Blood is thicker—On TV
Black
Deep Space Nine (Cardassian)
Dr. Who (Nostrovines)
The Outer Limits: "Promised Land" (Tsal-Khan)
The Outer Limits: “The Outpost” (Talon)
Smallville (cyborg Victor Stone)
Blue
Deep Space Nine (Andorians)
Deep Space Nine (Bolians)
Falling Skies (Espheni)
Farscape (Nebari)
Humans (Synths)
Power Rangers: Kaizoku Sentai Gokaiger (Basco ta Jolokia) (Bluish/green)
Stargate SG-1 (Goa'uld)
Green
ALF (ALF)
Dr. Who (Sontarans)
Dr. Who (Kaleds) (greenish/purple)
Dr. Who: “Warriors of the Deep” (Sea Devils)
Dr. Who: “The Crimson Horror” (Mr. Sweet)
Dr. Who (Daleks)
Dr. Who (Davros)
Dr. Who (Foamasi)
Dr. Who (Ice Warriors)
Dr. Who (Meep)
Kamen Rider Blade (Undead)
Kamen Rider Decade (Undead)
Kamen Rider Zi-O (Undead)
The Outer Limits: "The Voyage Home" (alien)
The Outer Limits: "A New Life" (Father)
Star Trek (Vulcans)
Star Trek (Romulans)
Stargate SG-1 (bounty hunter)
V (visitors)
X files (alien/human hybrid)
Pink
Defiance (Castithans)
Purple
Falling Skies (Volm)
Dr. Who (Ood)
White, Milky or clear
Babylon 5 (Drazi)
Defiance (Indogenes)
Dr. Who (The Silent)
Dr. Who: The Tomb of the Cybermen (Cyberman)
Farscape (Luxans)
Stargate SG-1 (O'Neill)
Teen Titans (cyborg Victor Stone)
Yellow
Dr. Who (Judoon)
Dr. Who (Mayflies)
Dr. Who (Waro) (yellow/green)
The Outer Limits: "Manifest Destiny" (Trion) (yellow/green)
Other notable blood
In “Angel” episode "I Will Remember You" Angel is "infected" with demonic blood that cures him of his vampirism. It's bright neon green.
In “Andromeda” the android Doyle "bleeds" superconductor fluid when cut. Due to her in-built Weirdness Censor, she sees it as ordinary blood, thinking herself human.
In “Buffy the Vampire Slayer” episode "Earshot", a mouthless demon's fluorescent blood splashes onto Buffy's hand and gives her an "aspect of the demon", which apparently is hearing people's thoughts.
In “Doctor Who” Time Lord blood has been subject to Retroactive Continuity: In "State of Decay", the Doctor's blood is blue. In every other episode of the series where he (or other Time Lords) bleeds, it's red. Reportedly, Fourth Doctor Tom Baker insisted on his blood being blue in that story for reasons known only to him. The Expanded Universe goes with the idea that Time Lord blood is just a little bit brighter or oranger than human blood. It's sometimes described as basically red, but "orangey". (This was partially an attempt to explain away the slightly too bright fake blood used by the BBC's special effects department in the 70s.) In the movie it's red, but is different enough from human blood on a cellular level that Grace describes it as "not blood" when she looks at it under a microscope.
In “Farscape” Luxans have clear blood which turns to black when they get hurt. Black blood is toxic, thus the bleeding has to be stimulated until it turns clear again. Delvians, being humanoid, sapient plants, bleed a sap-like substance.
In “The Outer Limits” episode "The Grell", the titular race's blood can alter DNA, meaning that a human who is exposed to it will turn into a Grell.
Blood is thicker—In Real Life
For the most part most insects, or exoskeleton animals, have yellow blood. Some do have green blood and crustaceans usually have blue blood. For example:
Blue Blood
Clams
Horseshoe Crabs
Lobsters
Octopuses
Scorpions
Slugs
Snails
Spiders
Brown Blood
Pinna sqamosa mollusk
Green Blood
Leeches
Skinks
Purple Blood
Brachiopods
Peanut Worms
Priapulida Worms (penis worms)
White, Milky or Clear
Cockroaches
Icefish
Yellow
Beetles
Insects
Sea Cucumbers
No Blood
Corals
Jellies
Sea Anemones
Sponges
Worms (some types)
Blood is Thicker--In Humans
For the most part human blood is red. Oxygenated blood is bright red and deoxygenated blood is dark red or maroon. However, there are certain circumstances where human blood can take on different colors. Carbon monoxide poisoning turns red blood even redder to the point where it is an unnatural shade of red. Sulpher can turn human blood green.
Blood coughed up by victims whose lungs have been pierced will be foamy and pink. A genetic disorder called Methemoglobinemia will make the blood appear blue or brown. Gallium can and will take the place of iron in the red blood cell, turning the hemoglobin blue.