Similar spellings:
* Colyn
* Colen
* Cullen
* Kolin
* Colinn
* Collin (with a double "l")
Variations:
* Colin (most common spelling)
* Collen
* Cohlin
Foreign spellings:
* Colín (Spanish)
* Colin (French, German)
* Kolín (Czech)
It's important to note that the most common spelling is Colin. The variations are less common, but still exist.
Ultimately, the best way to spell the name is the way that the parents choose.