Could you use long strips as the individual pieces and soak each strip in stain for a progressively longer amount of time to create a gradient effect in the final product?
You really don’t want to seal a cutting board with anything other than mineral oil and beeswax. Stain is pretty toxic - wouldn’t want that to leach into your food.
Stain is almost always for coloring, not finishing (not clear if you were implying otherwise). There are products marketed as "stain" which are made from linseed oil and beeswax, but they really only darken the wood a little. General Finishes sells a "food safe, oil-and-urethane-based" stain for turned wooden bowls, it says it's low-VOC and PFAS-free. Personally, I love the aesthetic of food-safe linseed or other nut/seed oils, and simply use wood of the color I desire.
You'd be better off selecting pieces of wood that are compatible with each other and have natural color variation, then order them from dark to light to achieve a gradient. Or change the width of strips to create a "dithering" effect. You certainly don't want to use stain on a food-grade surface.
Not exactly what you're asking for but sand-shading is done over short distances to get gradients in marquetry and inlay work. Holly is a popular wood for the technique.