A good strategy for problems like this is to start by doing a simpler version. Suppose there was one heart that could be colored "red, pink, or blue". How many ways could it be colored? That should be easy! Three, of course, R, P, or B (writing "R" for "red", "P" for "pink", and "B" for "blue", of course).
Suppose there were two hearts. That's only a little harder- you might write out each possible combination:
RR
RP
RB
PR
PP
PB
BR
BP
BB.
Notice that I have taken the "R", "P", "B" for one and appended the same three letters for the second.
How many is that? You could make the same kind of chart for three hearts, taking each of those with "R", "P", or "B" added to the end- but you should be able to see a numerical pattern.
Do you know the "fundamental counting principle"?