Regex for hexadecimal colors

To answer the question, here is the version with regex :

#?(([0-9a-f]{2})([0-9a-f]{2})([0-9a-f]{2})|([0-9a-f])([0-9a-f])([0-9a-f]))

This Regex separates by 3 groups of two hex characters, or 3 groups of one hex character each.

To use the output without too much complexity, you can concatenate groups 2 and 5, 3 and 6, 4 and 7 respectively, as only one of each pair is filled.

#?(([0-9a-f]{2})([0-9a-f]{2})([0-9a-f]{2})|([0-9a-f]{3}))

This is the "original" question, with 3 or 1 group.

Simple and straightforward version without regex :

For this type of problem, I think regex although it seems to be shorter, is of unnecessary complexity, both to be processed and to be debugged, so I decided to put this basic example using programming "traditional".

It works with or without # at the beginning, and with 3 or 6 digits.

color = "#bacc01"

if color[0]=="#":
   color = color[1:]

if len(color) == 3:
   r = color[0]
   g = color[1]
   b = color[2]

else:
   r = color[0:2]
   g = color[2:4]
   b = color[4:6]

print( "red  ", r )
print( "green", g )
print( "blue ", b )

Output:

red   ba
green cc
blue  01

To adapt to #abc you can leave in a group only, just change whatever is inside the if inicial.

Here's the expression:

^#((\w{2})(\w{2})(\w{2})|(\w{3}))$

I basically added a new condition for the 3-character case, and also a $ , indicating that the string should end there.

As a bonus, here's an expression to detect a color string with 3 or 6 characters (but not the 3 groups):

^#(?:[0-9a-f]{3}){1,2}$

This expression should work for you:

^#?([0-9a-fA-F]{2})([0-9a-fA-F]{2})([0-9a-fA-F]{2})|([0-9a-fA-F]{3})$

It will return a color group as #fff 333 #333 . Or else, it will return three groups for colors like #ffffff ff33FF #333333 .

Note also that the expression has the character ^ at the beginning of the line and the $ at the end, it is at your disposal to remove them. This expression accepts only hexadecimal characters and # is optional.