I've always believed that yellow/orange speed signs were advisory and a suggested speed, and that any speed stated on a white sign was the law.
So a yellow ramp sign should be no different. There are some white ramp signs in the Edmonton area (most are, some newer ones are yellow).
But there's an interesting question that I've always wondered about that's tied to the whole yellow sign on a ramp thing: Let's say the freeway's speed limit is 100, the road you are exiting onto has a limit of 50. The ramp sign suggests 70 (because it's in yellow), but technically, it is not a speed limit. Does that mean the ramp's legal speed limit is 100? It can't be 50, since that's lower than the 70 suggested? Or is it "sky's the limit" since there is no limit on the ramp?