one problem and a potential problem?

so today, i get home from work and go check in to see how the babies are doing, and to my surprise i notice bugs. yep. i am pissed. from what i can tell they are aphids? they are crawling on it, but i don't actually see any munching yet. trying to squash one for magnification was near impossible, and i tried lol. i caught one under the mag for a second, he seemed white, translucent and quite small.

as for the problem i am not too sure about, discoloration in my seedlings. these are the same seedlings with the aphids, they are only a little over an inch tall still, and only been out of the soil for about 3-4 days now. through a little experimentation i transplanted one into a 3gal pot, one into a much smaller pot, and left one in the jiffy pot (that one seems stunted, probably just gunna throw it out since this is an experiment run on a time limit). My question is, as of yesterday and today, the center of the plant has started to lighten, much lighter green than the rest of the seedling. neither of the others are showing this change. is this normal? is it a sign of a deficiency this early in the game? ill try to get a pic (of both the aphid and brightening of the pigment) but my camera isn't that good, and doesn't seem to want to focus in on something so small.

If your using mg soil it could be gnats.

I dont believe they hurt your plants. you can rid of them by put a half inch layer of sand on your soil. cover it completely it suffocates them.

At this stage i Recommend using insecticide soap, By the time your plants are mature the life cycle is broken and there is no trace of soap on your buds.

jiffy pellets hold a lot of water, if your not allowing your soil to dry you will damage your roots,fungus gnats will thrive in soil that is too moist

thanks for the replies. the soil is definitely dry, i dunno if its my extremely low RH (usually somewhere in the teens) or the heat, which at times can peak 85, but my pots are usually dry. i can dump a cup or 2 of water in each one (including the one thats just in the jiffy pot) and they will be bone dry in a day. and no, not just top soil, but upwards of 3 inches down will be bone dry as well. i fear for overwatering, so iam trying to make sure i dont do it often, only at signs of needing it. is droopage what i should look for there?

oh, and no comments on the light green center of the dominant seedling. i take it this is normal? or at least nothing out of the ordinary? thanks a ton again for the responses.

-Edit- and ya, i actually am using MG Organic so that was my thought, but most of the pics ive seen of gnats are not the greenish color these seem to be? ill definitely be looking into the sand idea here soon.