basic chemistry question: what is the relationship between absorbance and wavelength?

absorbance is most likely the wrong word to use in your question. You are talking about absorption. It refers to the physical process of absorbing light, while absorbance refers to the mathematical quantity. Two different things.
So I assume you mean  absorption.

So  if I understand your question correctly, you are right. The eye sees that wave length and translates it into red in the brain. The light source must have the red wave length with it for the object to reflect the red waves. If the object is lighted by a blue light it looks black since it absorbs every other wave lenght except red.