Final answer:
Ava will likely see a dark brown or black color when she looks through a blue lens over a red lens, as the lenses filter out complementary colors and block most of the visible light spectrum.
Step-by-step explanation:
When Ava places the blue lens of one pair of 3D glasses over the red lens of another and looks through both at the same time, the color she will see is most likely dark brown or black. This is because each lens is designed to filter out its complementary color (blue filters out yellow, and red filters out cyan, which contains blue). When the lenses are combined, they collectively filter out most of the visible light spectrum, allowing minimal light to pass through, which will make it appear very dark.
Typically, 3D glasses are designed so that one lens only allows red light to pass through while the other allows only blue (and sometimes green) light to pass through. When layered, they could potentially block all light that would normally reach the eyes. The exact color perceived can vary depending on the specific shades of blue and red used in the lenses, but it typically results in a very dark color because there is very little overlap in the light spectra that can pass through both.