Changing Color

What does it mean, when your leafs change from pretty healthy green, to a light greenish yellow?(not all just the two at the bottom?) ill edit with pictures after i shower...

Here are some pictures i took, you can see where the bottom leafs are turning light greenish yellow. I hope there not permantly ruined this is my first grow...and only plant. is a better picture. the flash shows alot more detail

Do you ph your water? Have a fan on that sprout?

mine do that. i think they are just using up the energy in the starter leaf. mine yellow then die off.

It's just the cotyledon's drying up nothing wrong

sorry for butting into this thread, but just wondering, this has happend to my plant also. when the cotyledon's die off, and go yellow/brown, is it time to start feedng?

i have Miracle Grow All purpose plant food 15:13.1:12.4 and it says to use one small scoop, to a litre of water...therefore, should i mix it to 1/4 strength? so 1/4 of a small scoop to one litre of water? is this plant food even use-able?

and i also have POT 'N' PEAT Potting Mix, newbie question, but is this ok to use for a new growing medium when i transplant it out of its small pot into a larger one? and is it a soil? like would i need to add soil to the pot n peat? or is the 'pot' part meaning soil? confused, new to this..

im also in the process of making a diy reflector out of cardboard, and ill b lining it with the same stuff i have put up around my grow box, its the reflective side of a car shun shade. seems to work well.

please, first timer, new to this, needs advice and help please???

looks fine, it almost always happens. Btw, ur soil looks, well, sub par is putting it nicely. Wat kind of mix are u using?