Amazfit Watch faces

I am new in designing watch faces. I would appreciate if one tells me how to use correct colors for background and foreground objects. For example, if I try to assign red color to a font in a group of digits then warning message is shown during compilation. Consequently, the watch face objects doesn't show up correct and smooth color. Instead a grainy color is displayed. I know there are a fixed number of colors available for using in watch face designs. I normally use windows paint application to apply color to my watch faces. I suppose at least 100% Red, Yellow, Blue, etc. should be acceptable colors but why warning message appears during compilation of the watch face? Thanks in advance.