There isn't a uniform standard as far as I can tell. If you look at filmtools' stingers, they do white for 25', red for 50', and yellow for 100ft, with no color for 10ft (which makes sense, it's easy to ID the length when it's that short). A rental house I've worked with a lot does orange for 25ft, yellow for 50ft, and no markings for 100ft.
I've also seen the PRG color code system on the internet, which goes like this:
There are also color codes for DMX cable, if you or others on your crew use DMX frequently you might copy that so as not to have two separate systems to memorize:
5ft - red
10ft - yellow
15ft - green
25ft - orange
50ft - white
100ft - purple
If there's a rental house that you use to supplement your own equipment for bigger jobs, it makes the most sense to copy whatever system they use.