Can Color and Black-and-Grey Tattoos Work Together on One Arm?

You can keep a color tattoo beside black-and-grey work. The next decision is how they should relate: separate pieces with open skin between them, or parts of a connected arrangement. Look at the whole arm before choosing a background to join them.
What can connect different palettes?
Similar scale, repeated shapes or a limited accent color can create continuity. Open skin can also preserve a deliberate separation. Connecting every piece with the same background is only one option, and it may change the character of the tattoos you already enjoy.
The pale blue eye in William's Lion, thorns & cross offers a small-scale example of color within black-and-grey work. A whole-arm plan needs another step: seeing that kind of accent beside the actual tattoos already there. Bring full views of them, not just close crops.
Should the newest tattoo match the darkest one?
Not automatically. Matching only the darkest area can make the entire collection heavier than intended. Compare the distribution of dark and light regions, the size of the subjects and how much empty space remains between them.
Bring full-arm views rather than separate cropped pictures of each tattoo. Identify the pieces whose boundaries should remain clear. If you want a new color piece to be the focus, say that; if you want it to sit quietly within the existing work, the palette and scale need a different conversation.
Test the accent in the whole composition
A repeated accent can contribute, but it cannot solve a crowded placement or several competing subjects on its own. Evaluate the whole composition before deciding that each existing piece needs an addition.
Bring views of the entire arm to your consultation with William in Tulsa. Include the tattoos you want to remain separate as well as the ones you hope to connect.