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So this is what is happening with my tomato plant that is cut from a hybrid tomato from the store, and planted.

OK, so it is recognizably a tomato sprout now. Given where it is now, it should be producing its first ripe tomato a little before Thanksgiving, except of course it will be frost killed well before that.

It looks a little yellowish unless it's a trick of the photo.
I'm thinking it may be due to the chunky woody -- looks like mulch? -- planting medium which may be tying up the nitrogen. You can fertilize now since the true leaves are out. If using one of the blue etc salt mixed with water liquid, then yes at 1/2 strength.

Since this is seed from a hybrid, there's no way to know for sure what the growth characteristics will be -- determinate, indeterminate, early, late, size of the plant etc. but I'm sure that was discussed before in the other thread: Subject: Grow tomatoes from fresh?