I learned about RGB and RGBA while reading how to define colors in Cascading Style Sheets.
RGB is one notation through which colors may be set using a style sheet for a webpage. The
rgb() function takes three numerical values separated by a comma and each representing the colors Red, Blue and Green in the respective order.
The values can be between 0 and 255, inclusive.
The above example represents a shade of Green.
rgba() function, one may control the alpha channel to adjust the transparency. The function requires a fourth numerical value which can be a decimal value between 0 and 1; the latter being complete opaque and 0 meaning full transparency.
Applying a 50% transparency to the above example would give us:
Notice, how the Green further changes its shade.