Kidney stones come in a variety of clors, shapes, sizes and textures. Depending on how big they are, you may be able to see them. If they are very big you could sure feel them.
Kidney stones can be different colors depending upon what they are made of. They usually look like tan or black sand. You would need a proper collection cup and strainer and you still might not be able to see them.
Kidney stones come in many different colors and sizes. They are often yellow or brownish but some can be black, tan, or gold colored. One can look drastically different from another so it might be worthwhile to image search a few examples.