Attached are two examples of number lines with multiple color lines above and on the number line. (Algebra II - two of these number lines in the entire book.)
The colors are significant only in that they show the reader how the red and blue lines match to the two different formulas shown, and how the purple line is the result of the 'overlap'. The dotted lines show where the beginning of each colored line starts and 'drops' to the original number line, resulting in the purple 'overlap' line. These are my word as the print text does not say anthing anywhere in the book.
How should I represent this tactiled number line system?
I checked with the some of the BANA & NBA Nemeth committees and here is our combined response:
Represent the main line with braille dots as we usually do, but use a tactile method to do the additional lines.
Since the red, blue, and purple lines printed ON the main number line represent each SOLUTION, standard braille format for number lines is appropriate there.
The colors, as you say, are insignificant so they do not need to be identified. Using a tactile method for the other lines will work nicely. I would braille each inequality label aligned above each arrowhead.