Hex color notation have an alpha channel

The hex color notation can be described as #RGB[A] or #RRGGBB[AA] - it accepts an alpha channel that can be used to represent the transparency.

When using it as #RRGGBB[AA], the alpha channel is a hexadecimal number where 00 is full transparent and FF full opaque. If using the shorter #RGB[A] notation, it is a hexadecimal number ranging from 0 and F.

#FF7f00 /* orange */ #FF7f0000 /* orange 0% opaque */ #FF7f0080 /* orange 50% opaque */ #FF7f00FF /* orange 100% opaque */ #01E /* blue */ #01E0 /* blue 0% opaque */ #01E8 /* blue 53% opaque */ #01EF /* blue 100% opaque */ 

You can find out more on MDN.

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