Do you have photos? Is that all the leaves since you got the plant? And what sort of time scale are you speaking about?

katsols, I'm having a similar issue with my marantas...not sure what's going on. I read up on it and thought it seemed like a nutrient problem, but with a little more frequent fertilizing, they're still having issues...good luck! I'll be checking back to say what people think it may be so I can learn something too!

FF

Sorry for late reply, i thought no one did and thank you.
Here is a photograph.
A comparison, darker leaf, one of the leaves it originally had when arrived and the pale one which are the new leaves that it grew out. And what do you mean by time scale? how long ago i got it?
{{gwi:76165}}

I'm not sure that's enough light. That's not the same Cal I have but mine spent the winter in an east window, getting direct sun all morning. Weekly sounds extremely often for fertilizing, but I'm not much of a fertilizer user, at best I do it sporadically during summer.

Love the pink spots on the older leaf! That's a beautiful plant.

ok i'll try giving it more light, thank you =] i thought it was the opposite pale because too much light form my grow light.

The new leaves are usually light in color and darken as they mature.

That's what I was wondering too, whether it just needed a bit more time to darken up. Hence the question about time scale, what length of time this had happened over. Your leaf does look a bit too yellow, don't know if that's the camera, or the plant. This is a photo of a new and old leaf (looks to be the same Calathea as yours) of mine that I took tonight.