An undershirt is "un maillot de corps / un maillot", "un T-shirt" (when it has sleeves), or "un marcel" (for a wifebeater) in French.
You can also use "la veste" (which is like a vest, jacket or coat) or "le tricot de corps" (which is like a undershirt, singlet, vest)
Undershirt.
Undershirt?
undershirt
Vest
White. They say it may distract the hitter because the ball is also white.
an undershirt
I believe you wear the white undershirt. ("technically" you could wear any undershirt you want, just saying.) Why would you want to have the collar from the khaki blouse underneath that coat's leatherneck collar? Doesnt seem right to me. Plus when they were issued to me, we were told to not wear the blouse under it and just the undershirt.
Undershirt Underwear
blue of course
an undershirt or nothing
to say is the verb 'dire' in French.