I have tried anthotypes a couple of weeks ago. It goes about as fast as the bleaching of a newspaper in the sun. It's a bleaching prosess, so you start with dark shaded paper and sunlight makes the exposed parts lighter. You need an inverted negative with as much contrast as possible. Your a4 transparency is a great way to do this. It doesn't matter if it's b/w or colour, the outcome would be a two toned anthotype.
My experiment with anthotypes didn't work because of two main resons. It was winter. You need as much sunlight as possible, preferebly direct sunlight (or uv light from a solarium). Second, the paint I used was made from dark purple flowers and ordinairy tapwater. Before I could apply several coats of paint, the paint had gone bad. Better is to use alcohol.
Apply the paint as even as possible and keep both paint and paper in a dark place to prevent unwanted exposure. Use paper that can withstand a couple of wet coats of paint. I've found some help on an alternative photography website, but it was just some guidlines. Every anthotype is different.
My experiment also involved using a anthotype paper instead of film in a DIY large format camera, but it didn't work. The regular anthotype didn't work either, so next summer I'll give it another try.
I'm going to wait untill spring/summer to try again.