Do they sell river rocks/pebbles that come in different colors other than the tanish natural-looking color ? I'm hoping to change my substrate.

I have river rocks in a few colors - an almost white, to brownish, greyish, and black. Found those in the craft stores. I think the ones you can buy in the garden section of HomeDepot have a more uniformed boring color...

Then would something like this be safe?

Hm, there are an aweful lot of chemicals in that kit. Polyurethane, the paint, concrete and such, I wouldn't trust them being fish safe. They might be fine for dry areas, but you never know what that stuff releases once its exposed to water all the time. Some might tinker with the water chemistry as well, like changing the pH up- or downward.

If you have a company locally that supplies rock for landscaping and such, you can arm yourself with a bottle of vinegar and a pipette. Once you find something you like, drop a few droplets of the vinegar onto the rock and see if it reacts. If it fizzles like soda, that a no-no....

I have japanese pebbles in my bare bottom tank.I have black and cream ones.I also have dazzle stones which come in pink,yellow,blue and green.

Then maybe this would be safer.