The patent rules provide that black and white line drawings are normally required for patent drawings. 37 CFR 1.84(a)(1). There is a rule for filing drawings in color, but it requires filing a petition to allow color drawings and paying a fee (for a utility patent application). MPEP 608.02(VIII). Instead of going that route, you can use certain back and white lining patterns to show color according a USPTO key, which is shown below.
This key is provided from MPEP 608.02(IX). Providing the lining pattern on a surface or portion of an element of your drawings will indicate that surface or portion has the corresponding color. You will also want to provide a text description of the drawings indicating that the drawing is lined for color, for example, “portions of the widget 8 of Figure 1 are lined for the color blue.” Or you can be more specific, particularly if multiple colors are lined in the same drawing, such as “the front surface portion 10 is lined for the color blue and the back surface portion 12 is lined for the color orange.”
The lining key is useful for showing color. But if it is important to show a particular shade of a color, then the linking key will probably not work. In that case, you will likely need to follow the rules for filing actual color drawings, petitioning, and paying the fee (for a utility patent application).