That could be a series of trips, as in base 3 digits that just happen to be grouped five at a time, like encrypted text often is.
If you break it down as 3-trip code points, there are 27 possible codes, which is ideal for encoding english text plus a space.
000, 001, 002, 010, 011, 012, 020, 021, 022
100, 101, 102, 110, 111, 112, 120, 121, 122
200, 201, 202, 210, 211, 212, 220, 221, 222
_ A B C D E F G H
I J K L M N O P Q
R S T U V W X Y Z
So the question is, which color represents 0, which is 1 and which is 2?
And then how do you group them. Horizontal of vertical sequence. I suggest that the 5 rows is a hint to go vertical which then leaves two possible variations, left to right or right to left
xya
xza
xzb
yzb
yab
Would be xxx yyy zzz aaa bbb codepoints