"prograde and retrograde" (yellow ones) are basically "outwards" and "inwards" respectively, (the blue ones are "left and right" and the pink ones are "up and down").
because your spaceship (aside from being awesome), is "floating about in space" - there is no "up down left right etc", because space has no "centre" like the earth does, and if something has no centre (no gravity to pulling towards), then there is no such thing as "up and down"; such is space.
...so some guy called them "prograde and retrograde" etc (annoying).
i have trouble too, i can't even remember what the pink and blue ones are called...
if you learn the function of (from the tutorial etc), then you don't need to remember the names, fortunately! (because if you needed to remember everything in game, then the game would suck big time... (imho))