Offering the various colors and the options to modify is a move in the right direction, but as is -- these colors will be disorienting.
LATE: Changing from Pink to Green is not only going to confuse users used to the pink, but Green is also misguiding as it's a positive or affirming color elsewhere in a Canvas and related technologies. RECOMMEND: Keep Pink.
MISSING: I trust assignments will only appear missing if they're past a due date. Otherwise, I'm not sure how this works. Color wise, pink is confusing b/c is used to mean late. RECOMMEND: A darker pink given it's the next stage after Late, which should remain pink.
RESUBMITTED: Perhaps blue would work for this...As is, it's too close to Missing.
DROPPED: Keep the light gray that is in the current grade book.
EXCUSED: Keep the EX and light gray. Adding additional colors is a serious overload here.
I agree with your thoughts about the color choices. There is another option, however. You can customize the color for each status. At the bottom of the dialogue box where you assign colors to different statuses, you see a color hex number. If you search color hex code online, you can see the code for various color options. The only problem is, it is hard to change the code before the box disappears. It is a bug that I've reported. The way I was able to work around it was by holding down the right click button on the mouse while entering the hex code. I was able to change all the color options for the statuses and I'm quite pleased with the results.