Why is the photograph in a blue tone?

Original:

New:

Camera: Nikon DX

Your white balance is not set correctly.

Match the cameras white balance to match the lighting falling on the scene

If you shoot in RAW, you can later balance the white balance before exporting them as high resolution JPEG files

The white balance appears to be off in both - in the first the tones are a tad too 'warm' (slightly yellow) & in the second, they appear too 'cool' (slightly blue).

The second shot looks a bit underexposed to me if the paper is supposed to be white (it looks grey).

If you can shoot in raw, then it's easier to adjust wb in post.

Really nice drawings btw!