Anchorage is 14.5 hours behind Colombo
Best overlap: 8:00 AM to 9:00 AM in Colombo is 5:30 PM to 6:30 PM in Anchorage.
For the smoothest call, aim inside 8:00 AM to 9:00 AM in Colombo, i.e. 5:30 PM to 6:30 PM in Anchorage. The overlap barely stretches to 1 hour, so reserve it for what really needs a live conversation and handle the rest async. The date rolls over between them: Anchorage is on the previous day relative to Colombo during these hours. Daylight saving complicates things slightly: Anchorage observes it, Colombo doesn't, so the difference flexes by an hour part of the year.