Leopard gecko turning dark yellow

Question
Is it normal for a leopard gecko to turn dark yellow?  This is my grandson's pet and I have had it for about a year.  Still a little in the dark about how it should look.  Won't eat gecko food but will eat live crickets and dead crickets.  Have to be careful to put only a tiny bit of calcium powder or it won't eat what has the powder on it.

Should I be feeding it fresh veggies or fruit?

Need a little help.  Don't want it to die under my watch.

Answer
Hello Cat,

Can you post a picture of the leopard gecko for me?
How old is he?  
They normally will eat only live crickets & worms, & are not interested in non moving prey.  You can put a small amount of calcium powder in a small dish in the tank for him or powder the feeders.
Are you using an undertank heater along with an overhead basking light?  
A dark yellow could just be partially due to improper temps or he is just changing colors as he matures.  How long has he been turning darker?
What type of substrate do you use, sand, tiles, paper towels, shelf liner?

Tracie