colour tube

NOUN
11 LETTERS · STARTS WITH C

colour tube is a valid 11-letter word worth 14 points in Scrabble and 19 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
C3O1L1O1U1R1T1U1B3E1
3 + 1 + 1 + 1 + 1 + 1 + 0 + 1 + 1 + 3 + 1 =14 PTS
DOUBLE WORD → 28TRIPLE WORD → 42
MEANING

What does colour tube mean?