If you're like me and are taking photos of your work on your phone, they keep coming out much too dark. It doesn't matter how much light you put on it. There is a way to post process the pictures to return the paper to its original whiteness or at least approximate white. See the examples below. The dark one was done on my camera phone, auto flash, and under bright lighting.
Do not fear, just open your picture in almost any image editor. I'm using Sumo. It's free but you probably have one that will do just fine on your computer. Once it's open, look for the "Adjustments" menu. Then look for something that says "balance/contrast" or something approximate to that. There you will find a slider bar that will allow you to adjust the contrast up and down. Adjust to taste. Make it white, but there are some other slight side effects that have to be balanced against.
So there you go you don't need to post those dark pictures of your artwork anymore. It does add a little more work, but it's worth it to present your art favorably.
Good luck. I hope it helps you.
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