explicit color vectors may not work with particle bbox clipping
at the moment, giving an explicit color vector for particle colors requires the vector to be exactly as long as the particle vector AFTER all filtering (the user-specified custom filterfunction and the default bbox intersection). This is conveninent for some applications (e.g. I have a vector of colors for the cells I want to plot and use a filterfunction to exclude the cells I don't want to plot), but does not work as soon as the number of particles that pass the filter isn't obvious a priori — e.g. when plotting secondary copies, which are by default clipped to the plot limits to avoid drawing unnecessary particles.
I guess the most consistent solution would be to always require the color vector to be as long as the particle vector before filtering, everything else is even more awkward. For me, this means I'm going to have to add some padding to the color vector for the particles I don't want to plot, but I guess I'll be able to deal with that