Yeah, on the harder to distinguish tests I just decipher what may be the lowest possible reading and the highest possible reading if the color could be seen as multiple different levels, then I sort of pic a color/level inbetween the high and low (sometimes when I do that though, I do narrow down what the color more likely resembles.
From your pic, for ammonia, I would say, ehhh, maybe .5-1ppm, nitrite .25ppm, nitrate pretty much 0ppm (has a little orange tinge though). Lighting makes a difference though.
How long you been cycling for? Know your temperature and pH?