Why is the photo not saturated enough? I use Nikon D90. Three Lamps District used in the studio mainly takes pictures of children.

Has the white balance been adjusted? Is the exposure accurate? If it is recommended to use a hand-held exposure meter for studio shooting, measure the light value and shadow value as a reference for adjusting exposure.

If movies and TVs use flash, set the white balance to daylight. If other lights are used, turn on the lights and put the standard whiteboard where it is photographed. After aiming with the camera, zoom to make the whiteboard fill the viewing frame, and set the white balance manually.

Judging from the photos you sent, there is something wrong with the lighting. The subject has no layering, and the exposure is not compensated (your background is white, which affects the accuracy of photometry). The best lighting in the three-light area should be that the main light is the brightest, followed by the secondary light, and the silhouette light hits the back and top of the subject.