Discoloured leaves from seed, any ideas why this happens?

This is "normal" and not an issue. No plant will ever have 100% perfect leaves, 100% of the time. New growth looks fantastic.

Soil too ritch, or you overfed her in young stage. Not a biggie, she grows, those leaves will go down when plant will be bigger anyways. Would not sweat , just feed a bit less.

I agree, it’s nothin to worry about. I had this a few months back, or well my plant did lol. Anyhow, it did give me weird colors and random light and dark green weirdness.. that later actually turned half red/half green (in flower). I thought stuff was wrong with it all the time, and actually even caused some problems trying to correct it. Yeah, it never went away and wound up being a great plant that has made some awesome buds. Good luck

Possibly "variegation" google for more info and images of how it displays in many ways .. should clear up on newer leaves more times than not. As long as it isn't pervasive and significantly impacts photosynthesis, should not be a problem. Possibly just some younger leaves with more blemishes.. i'm not sure if that light green falls under same term, but i believe it does. In either case, It'll most likely grow out of it. veriegation is not a big concern. Sometimes it's a bright yellow. still not an issue. the plants that have weird undiagniosable / untreatable issues with fucked up leaves etc etc.. throw those out.. this is not an example of that. All leaves showingn spots and blotchiness, maybe some wrinkles and other generally unusually physical traits.. some sort of disease or genetic defect in those cases. the outcome usually sucks.

As an afterthought. I’ve had it sort of like a two tone green. It could be genetics or maybe ph. Likely will grow out of it or won’t cause any harm but if ph then it’ll need sorting. They say 6-7 in soil with lower end in veg. You are on point but I’d advise try letting it drift so you vary it so nutes can be all uptaken. Also it’s your soil ph that counts more than solution ph. Dona 2:1 slurry test

Is it on just one or two leaves if so don’t worry. If on many I reckon magnesium especially if veins are still darker green. I’d say eh maybe a tad low for this age. I’m jealous of it tho in flower