Turlough O'Carolan was blind. It did not matter the color of his strings. His sightlessness might account for rumored shortcomings as a performer. It did not diminish his talents as a tunesmith and as a gracious guest (or flatterer).
Latin American string coloration came up in recent private correspondence, prompting me to think about string color and muscle memory.
Here are my perceptions (facts from my point of view):
1) Default key per "harplist" standard is C, C's are red, F's are blue.
2) Default key is F in Paraguay (per Nicolas Carter), F's are red, C's are Blue.
3) Default key is D in Colombia (per Hildo Ariel) and ... wait, let's not go there yet.
If the difference between Paraguayan and harplist standards is enough to confuse many of us, I suggest that many of us (myself included) are overly dependent on watching the strings.
Naming of "default keys" does not imply no key changes. It's just that when the key is changed, the harpist must correctly adjust for color pattern changes. The pattern is not simply the individual string color, but its relation to the colors of adjacent strings.
Assuming key of C, in harplist standard, the tonic is red, the fourth blue. In Paraguayan, the tonic is blue, the fourth is red. Notice, however, that RED marks the "default" root in both (F in Paraguay, C in harplist standard). But while blue marks the FOURTH (F) in harplist, blue marks the FIFTH (C) in Paraguay. This accounts for some of our difficulties switching the colors.
Now, regarding string coloration in Colombia, Hildo explained that the only general consensus is that the D strings should be DISTINCTIVE FROM THE OTHERS. He adds there is some lesser consensus that the FIFTH interval (NOT the fourth) should be of the SAME COLOR as the tonic; so D and A should be the same color.
Just now at ALJ I surveyed 14 harps, tuned in D, to see whether colors were consistent with these principles. Most strings here are dark colored, red, blue, black and even green, but there are clear, yellow and orange strings here and there, and even VARIEGATED strings. (I could not survey 8 other harps that were in cases.)
To be consistent, the D's and A's SHOULD BE THE SAME COLOR, while other strings may be of any color EXCEPT that color. That distinctive color here at ALJ is YELLOW.
I could only judge TWO of 14 harps to be entirely consistent. The other 12 are "semi-consistent," showing various deviations. On these other harps it is not hard to see the D's and A's, when you look closely and get familiar with the particular instrument. Often the deviation is not hard to deal with, a wrong-colored D in the low range or clear instead of yellow in mid and higher ranges.
I could go on about tactics to cope with the situation, to build muscle memory. That might be another post. Here, I would note two points to take away.
1) The Colombian practice in "default" key of D marks tonic and FIFTH (A), not (as in "harplist standard") tonic and FOURTH (F). This is like Paraguayan in that (in "default" key of F) distinctive colors are given to tonic and fifth (not fourth). Habits from harplist standard will not work.
2) The main string we need to see is the root or tonic. From there, we can (or must) rely on muscle memory to find the other intervals.