COMBINATION VISION TEST
[[An Ishihara color blindness test (which typically consists of a circle comprised of dots of different colors, arranged such that someone with complete color vision can discern numbers) with numbers instead of colored dots. It is not easy to see, but the numbers show a large '42' in the center. The 4 and the 2 are made up of different numbers.]]
If you can see one big number but not the other, you have synesthesia 
and
 colorblindness.

{{Title text: If you see two numbers but they're both the same and you have to squint to read them, you have synesthesia, colorblindness, diplopia, and myopia.}}