I have found the Ayrshire Archaeological and Natural History Society (AANHS) a valuable source of general Ayrshire Historical Information as they are instrmental in publishing books and pamphlets and making them available for sale. I do not have a current address but they are on the web and searcheable.
I have a copy of "Ayrshire The story of a county" by John Strawhorn published by the AANHS at Ayr on 1975. It is an invaluable source book for the general history of the county.
On page 23 it notes many grants and charters specifically:
"For King's Kyle, grants were made by the king himself to lesser barons who owed direct allegiance to the crown. We have references only to Philip de Colville (Ochiltree) and Thomas Colville le Scot (Dalmellington)."
This relates to the 12th or 13th century.
I have wondered why the second Colville was specfically noted as "le Scot". Perhaps that this might have been a Norman "Frenchification" of Caldwell and and "le Scot" was used to signify that this person was a native Scot rather than the other who was possibly a "true" Colville from a Norman family.
For those pursuing the Straiton ancestry I note that Dalmellington is not far from Straiton
I note that the Colville's were "big" at Ochiltree and Lessnessock until eventually selling out to a Stewart and moving to Fife where they remained a powerful and influential family in Scots afairs.
The "Ragman's Roll" for Ayrshire was signed by a number of Colville's (various spellings but no Caldwell's. Again we might invoke Norman court French as the culprit but it is impossible to be sure as there were no doubt "real" Colville's also and no one has sought to draw them together apart from the obvious difficulty in a french speaking pronunciation of "Caldwell" which would have to be getting close to "Colville".