The Problem
I own two pair of Warby Parker glasses - one regular prescription and one prescription sunglasses. I often carry both, in their cases, in whatever bag or purse I have with me. There is no differentiation in cases between regular and sunglasses. 80% of the time the first case I grab isn't the pair of glasses I want as there's no way of knowing what you've got until you open the case and look inside.
The Solution
Because the problem involves a blind grab in a dark purse, my recommendation is to have textural differences between the two - one smooth case, possibly plastic, and one textured case. This would allow both people looking at the cases and those going by touch alone to differentiate which type of spectacles are housed within, and make more accurate grabs when going for them.