I don't need any because I too roast my own coffee. I think you are roasting robusta beans, so I'm not 100% sure this applies, but in general coffees from Indonesia end up with an "uneven" look, mottled and with variation between beans, even when roasted perfectly. This is one reason why Sumatran coffees are often commercially over-roasted and lose a lot of their character. I usually roast them just a little into "2nd crack", and they don't look anywhere near as dark as other kinds of coffee roasted to the same level.
P.S. I love all the different explorations you do with coating and paper negatives and coffee and different processes. I'm always happy to see something new and interesting in the gallery from you!