RGBA

What is RGBA?

RGBA (Red, Green, Blue, Alpha) is a color format typically used for transparent images. RGBA is based on the RGB format, but it adds a fourth channel called the alpha channel. The alpha value is normally used to quantify the amount of opacity a pixel has in an image. For example, 100% alpha means opaque (not transparent), 0% alpha means fully transparent (invisible), and 50% means half-transparent.

Of the common image formats, only PNG and WEBP support alpha channels and RGBA colors. Although GIF kind of supports transparency, it's limited to one fully transparent color, and it doesn't work the same way as alpha.

In rare cases you may find a special program that uses the alpha channel of a PNG image for some non-transparency purpose. This tends to be very problematic, because most image-editing software uses pre-multiplied alpha when compositing layers. This means that a fully-transparent pixel is always black, i.e. it has the RGBA hex code of #00000000. Consequently, you can't have a colored pixel that is also fully transparent. In these cases you need to find a way to export the image from the image-editing program without pre-multiplied alpha. Krita, for example, has a feature like this.