Take pictures with a photographic lamp. The camera is d90.

Gray cards use white balance cards, but really can't use white paper (multiple opaque cards)

Make sure the exposure is correct, switch to manual focusing, adjust the white balance to custom, press and hold the white balance key, the shoulder screen flashes, and the viewfinder is all white. Press the shutter, the shoulder screen will display good as a successful setting, and then you can shoot with this white balance. If you change the position of the lamp or add a reflector in the middle, you'd better customize it again.

Another simple method is to shoot in raw format, take a white picture (white balance card, gray card, white paper) for each scene, and then use software to correct the white balance later, and then apply it to all photos of this scene.