All black wetsuits to a predator animal (sharks and killer whales) looks like seals or sea lions.
The reason for the multicolor wetsuits is to prevent accidental shark attacks while diving. The Black with Yellow is the basic color or the Yellow Belly Sea-snake which most sharks will not eat.

The all black wetsuit is not a good color for spearfishing because you look similar to that of seals or sea lions, seals and sea lions also eat fish. The multicolored wetsuits may not be a dis-advantage because you will look like any other big fish..

I have not had any problem spear fishing wearing color diving equipment and have had sharks avoid me because the the colors that I wear.

If you really must change the color of your wet suit, you can try coating it with a black liquid neoprene cement.