This has happened to me for the last few years (MS since 1988) off and on. Mostly at the back of the knees, but feet too sometimes.

Moved to the Southern Utah desert to escape the life of clouds and rain in my lifelong home of Oregon. Blue skies beat dismal gray, but the cold thing didn't stay in Oregon.

I have never noticed any color changes, but I've also never thought to look.

It just adds to the fun, as my heat thermostat has been screwed up for the last few years too (i.e. when it's 100 out, I still feel like 80 or something).

Sorry I don't have any advice for you to make it better. For me it's just day by day (sometimes hour to hour, I guess). Hope you find a method to combat it!