Question

why venous blood is red in color even though it has deoxgenated blood?

Answer 1

Human blood is red in color, ranging from bright red when oxygenated to a very dark, almost blackish-red when deoxygenated.[3] It owes its color to haemoglobin, to which oxygen binds. Deoxygenated blood is darker due to the difference in color between deoxyhaemoglobin and oxyhaemoglobin.
The blue appearance of surface veins is caused mostly by the scattering of blue light away from the outside of venous tissue if the vein is at 0.5 mm deep or more. Veins and arteries appear similar when skin is removed and are seen directly.[4][5]