What is olo? Scientists say theyve discovered a new color never seen Multi Color Crystallized Background Free Stock Photo Public Domain Colour Wheel Spectrum Rainbow Free image on Pixabay Clipart 6 color beach ball. Colorful decorative small gravel stones of mixed sizes in the brightest vibrant colors, safe for aquariums and terrariums. These stones are completely inert and do not affect the pH or water hardness. Rinse well before use. To place your order, choose the gravel color and size from the drop menu above before adding to cart. Note: Product images are for illustrative purposes only. Due to differences in monitors, colors of actual product may slightly appear different to the shade shown on the site.