Only the bottom of my light arena is blue, so the light hitting the specimen from all sides is likely to be little affected. I think I get more color distortion from my lens (from a defunct black-and-white photocopier) than from the background. I've tried various colored backgrounds but blue seems best to me.

As for this springtail, I'll move it to T. minor unless you reconsider. When I described it as charcoal/brown I meant that it had both charcoal-grey and lighter brown spots or scales on it (not that it was a very dark brown, almost the color of charcoal). If this explanation changes anything for you, please let me know.