The damage I'm seeing in those lights are definitely sun damage. Though it is possible to repaint with transparent glass paint, we actually do not suggest painting the incandescent bulbs. Color matching would be difficult, and chipping may also become a factor. Since incandescent bulbs are relatively cheap, I would suggest replacing them.
A factor to consider if you are buying replacements is the dip count. Bulbs that have been dipped in dye more than once tend to hold their color longer and have truer color. A good retailer will tell you how many times their bulbs have been dipped. Double dipped and triple dipped bulbs make for great incandescent C7s and would have a longer life when it comes to sun damage.
Hope this helps!