Eliot use the color red in various places throughout the poem: in lines 25 and 26, speaking of the "red rock," at the beginning of Section IV, "after the torchlight red on sweaty faces," and in a few other places, too. Generally, red is symbolic of intense emotion, violence, and fire.

Another color Eliot uses repeatedly is brown, to describe the fog in line 61, to describe the land in line 175,and in a few other places. What do you think about when you think about the color brown as it occurs in nature? If a field is brown, there is nothing growing there, so there is a suggestion of barrenous and lack of growth in the use of this color.

The color violet is another color Eliot uses, in line 215, "the violet hour," and in line 379, "in the violet night." This color is generally used to describe something in the evening or night, and while it is difficult to know for sure, these are times that signify an ending to daylight, which is clear and good, so it is possible that the color violent is meant to show something that is ending or that is a contrast to the clarity and goodness of day,

There are other uses of color in the poem, and more examples than I  have provided here.  Quite often, when poets use colors as symbols, they are easy to understand because most of us see similar symbolism in these colors.

I hope this helps a bit.  Good luck to you.