Leaf color change and epsom salt question

hey everyone... the leaves on my plants are getting to be a darker green than the first set.. is this a problem? i was thinking not enough water, too much water? lack of neutrients? too much or too little light? any ideas or input??

Can you post a picture? Or check out the plant problems section in the growfaq at the top of the page, has pictures of lots of nutrient deficiencies.

i fed a plant some ep salt once and the leaves got really dark green. it seemed healthy tho. i hardly remember, it was my first attempt at growing.