If you are referring to why blood goes from bright red in the aorta to a darker reddish-purple in the pulmonary artery, the answer is because the blood has lost the majority of the oxygen it was carrying. This causes a conformation change in the carrier hemoglobin, which results in a color change.
If you are referring to another color change in the blood (such as why a particular animal's blood is chocolate brown, for example), this would be due to a toxicosis and the animal should be taken to a vet immediately.
Capillaries change color as they pass by body cells as the blood they contain loses oxygen. Oxygen-rich blood has a brighter color than oxygen-poor blood.
It can thin slightly in hotter temperatures and conversely thicken in colder temperatures. Blood is red and there may be very slight differences in colour in these cases but it would not be really noticeable.
Since blood is already liquid the particles would just mix together. Technically that would be dissolving.
In space, your blood is still red. The lack of gravity does not change the color of your blood. However, in a weightless environment, blood may behave differently due to changes in circulation.
oxygen
the of your blood after birth could be blue and red.
Blood changes color at the lungs because it unloads carbon dioxide and absorbs oxygen. Red blood cells that are carrying oxygen are a brighter red color than red blood cells that are depleted of oxygen.
Most vaginas with infections show no change in color. Trichomoniasis or candida can cause red vaginal skin.
vampires eyes change color when they are either a newborn or when they had drank a humans blood
When blood is exposed to air, it typically takes around 15-30 minutes for it to oxidize and change color, turning from bright red to a darker, brownish hue.
When you apply pressure to a fingernail, blood flow to that area can be temporarily restricted, causing the nail to change color. Typically, the nail may turn white or pale due to the lack of blood circulation. Once the pressure is released, normal blood flow resumes, and the nail usually returns to its original color as oxygenated blood fills the capillaries again. This color change is a temporary physiological response.
You skin changes color when it's cold because blood can't flow as easily.