The default "hydro" coloring in Foldit tells you whether the amino acid at a particular segment is hydrophobic or hydrophilic. The shape of the sidechain may tell you which amino acid is where, but there are times when a little more information is useful.
EnzDes and CPK make it easier to tell one sidechain from another. They also give clues about how the sidechains can form hydrogen bonds.
In both EnzDes and CPK, the sulfur atoms in cysteine and methionine show up in bright yellow.
Nitrogen atoms are dark blue, and oxygen atoms are red.
The last atom in proline's sidechain is a special case, colored in black, even though it's a nitrogen atom.