I am currently working on my dissertation and want to explore the role of competence as a mediator between the effect of colour of clothes on voting intention (focus on Western countries). Initially, I wanted to do a mediation analysis with colour (4 conditions) being the IV, competence the mediator (measured on a scale 1 - 9) and voting intention the DV (measured on a scale 1 - 7). However, as colour is a preset categorical variable I am looking for alternatives to mediation analysis. I am currently considering a one-way repeated-measures MANOVA but would be grateful for any suggestions and further help.
More details on the study design: I asked participants to rate "perceived competence" and "likelihood of voting for" using pictures of politicians wearing the four colours as stimuli.
Thank you in advance!