Add alpha transparency to any color and get rgba() values. Color Opacity / RGBA is a free online tool from the ToolsRift Color Tools collection. It runs entirely in your browser — nothing to install, no signup, and your data never leaves your device.
Pick a color, drag the opacity slider, preview it over the checkerboard, and copy the rgba() or 8-digit hex value.
Alpha is the opacity, from 0 (fully transparent) to 1 (fully opaque). rgba(0,0,0,0.5) is 50% black.
The last two hex digits are the alpha byte, so #FF000080 is red at about 50% opacity.
The checkerboard shows through the transparent areas so you can judge the true opacity of the color.