Color and keywords definition in atom


I am new in atom and I want to know the meaning of colors and keywords in atom
for example in auto-completion suggestions bar there are some icons on the left-hand side of that table like (f - v - c …)
or when my word is written in blue, purple, green or red what is the meaning of that color? Is this mean that it has wrong syntax?
Is there any guideline for this kind of information?