Say we have a double slit experiment. Besides the slit width, separation and distance from the detection screen, the color of light determines the fringe pattern spacing's. So red and blue have different patterns. Now if you take the same exact double slit experiment and fire electrons what determines the wavelength or pattern?
"the color of light determines the fringe pattern spacing"
Not the color, the wavelength. Yes, these ideas are coupled, but if you perform the experiment in a medium of non-trivial index of refraction, the fringes shift.1
And that tells you the property to use for particle version of the experiment: the de Broglie wavelength.
(You can also deduce this from how the interference develops: the two path from slit to screen cover different distances.)
1 This is roughly how gas indexes of refraction are measured, though they use a more powerful interferometer than a simple pair of slits.