Lead(II) iodate is white and lead(II) iodide is yellow.
The equations are
Human eyes can see only visible light ( wavelengths about 300 to 700 nm).
If all these wavelengths are present, we see it as "white" light.
A blue substance absorbs most visible wavelengths except blue, so we see it as blue.
Most substances, including lead(II) chlorate, absorb wavelengths that we cannot see and reflect the visible wavelengths, so we see them as white.
Lead(II) chloride is an exception. It absorbs all wavelengths but yellow, so we see it as yellow.