How to determine your skin undertone

Skin tones are often confused for undertones, but they are not the same thing
An undertone is the color that lies beneath the skin.You can have a cool, warm, or neutral undertone.

Check your veins

Green veins à warm UT

Blue veins à cool UT

Neutral

Other way is to think which color suits u the most Gold is for Warm UT and silver is for cool UT

 “cool” undertone:

Those with cool undertones will notice their skin has a pink, red, or blue tinge to it.
• If the veins on your wrist are blue or purple
• If silver jewelry suits your skin more than gold
• When you look at your skin in the sun, it appears blue-ish

Points to remember >“neutral” undertone:

If you have neutral undertones, your skin is neither pink/red/blue nor yellow/gold/peach, but somewhere in between.
• The veins on your wrist are blue-green
• Both gold and silver jewelry flatter your skin
• When you look at your skin in the sun, it appears greenish

Points to remember > “warm” undertone:

Those with warm undertones will notice their skin has a yellow, gold, or peach tinge to it. 
• The veins on your wrist are slightly green or olive
• Gold jewelry flatters your skin more than silver
• When you look at your skin in the sun, it appears yellowish

Below pics are taken from the web ..Hope it helps :)