Yellow, the complementary color of blue. The red is absorbed by the water, enough to make a visible difference with slightly reddened feet. Try it and see. Deep in water red is no longer present in light, so blood looks black. But there is plenty of red in a camera flash, so the blood looks red when so illuminated.
Blue illumination produces black.
A yellow banana reflects yellow and the adjacent colors, orange and green, so when illuminated with any of these colors it reflects that color and appears that color. A banana does not reflect blue, which is too far from yellow in the spectrum, so when illuminated with blue it appears black. The reflected color is white minus red, or cyan. You see the complimentary colors due to retina fatigue. The blue will appear yellow, the red cyan, and the white black.