Hi Kiwicousey,
I tried searching for you at "scotlandspeople".
The search engine really doesn't like "Colin Thom".
I checked the 1851 census when he would have been about 17
I put in "Thom", exact, "Col*n", male aged 10 - 20, all records, all districts and got 1 result.
The * means wildcard, maybe you could resort to this type of search, I don't think Colin Thom would be a common name?
You might find his birthplace this way, perhaps he was not born in Fife or Perthshire

.
Lots of my Granfathers WW2 stuff had Perth, Fifeshire written on it (which I alway thought was weird, perhaps it was were all the big ships left from?)
My family uses the Wemyss middle name in New Zealand too, but my grandmother brought it out in the 1940's to Auckland, so your ancestor might bump into ours (Wemyss, Clark)!
I think I'll give up too for now as I can only do a free search, I used up all my credits at the paysite on my lot!
Melissa