Your hex value does not accept uppercase values. Might I suggest this instead:
#([a-fA-F0-9]{3}){1,2}\b
Neither of ours accepts 8 character Hex values (transparency in 7th and 8th characters).
I have some more to share:
Match the 'src' for images
\< *[img][^\>]*[src] *= *[\"\']{0,1}([^\"\'\ >]*)
Match ID's for Youtube Videos
/http:\/\/(?:youtu\.be\/|(?:[a-z]{2,3}\.)?youtube\.com\/watch(?:\?|#\!)v=)([\w-]{11}).*/gi
Match CSS comments
\/\*[^*]*\*+([^/*][^*]*\*+)*\/
Match every word except words in list:
\bTarzan\b|\bJane\b|\bSuperman\b|(\w+);