A colour change in a plastic item can be distinct from food remaining on its surface. The material and its care instructions should be considered before interpreting the appearance as a machine fault.
Understanding this situation
The dishwasher cannot guarantee that every food pigment leaves every suitable plastic unchanged. A hotter cycle or stronger chemical may be unsuitable and can create additional damage.
A useful next step
Follow the item maker's guidance for cleaning or staining. Do not mix products or repeat harsh cycles to restore a colour. Report whether there is actual residue, smell or a broad change in washing results alongside the discolouration.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.