Well, that's a horse of a different color. Seems like the long way around when dv8's method is more standard. OTOH, I can understand a teacher wanting you to understand the concept of layer masks by having you discover many uses.
My method may not yet be what he wants. I have to assume that your kayak has a layer mask. That makes all the difference to the task he has given. But bear in mind, what you will learn as you go is that there is rarely one one way to do something in PS.
What I have done is make a selection of the lizard and put on a layer mask to "mask" out the background. Then I made a copy of this layer and the mask. Next, I made a blank layer above that and filled it with color. Then I activated the mask on the lizard layer by ctl/cmd clicking the thumbnail. With the color layer selected and the marching ants displaying, click on layer mask and the blue will now have the same layer mask as the lizard. Oh, in your case, the kayak, lol.
Adjust the blend mode and opacity till you get the color result you want. You may have to change the color to actually achieve the proper hue, unless you start playing with adjustment layers. I used vivid light at 100% opacity. Some modes may give a flat look to the image and some will alter your color considerably. Even vivid light will need adjustments for loos of highlight.
This is a good exercise to learn the blend modes a bit too, though it helps to understand how they are grouped and why they do what they do. Blah, blah, blah.
Hope this helps.