What do the different color filters for the holga do to a B&W photograph?
I just bought the filter set for my holga and I was wondering what some of the different filters do. For instance does the green filter add color to a subject like it would for a regular film camera? Or does the red add contrast to the sky? Or do they do completely different things?
You are right, the different colour filters will change the look and "feel" of your B&W photo.
Instead of writing a super-long description of what happens here, I would suggest using a program such as Adobe PhotoShop (any version) or any photo editing program you have, converting a colour photo you are familiar with from colour to B&W, and then playing with the colour levels.
In Windows Photo Gallery, which most PCs come with nowadays, you would just open the photo, click "Fix", "Adjust Color", play with the "Tint" (set it to very red, or very green) and bring the "Saturation" to zero. When you know what moving the "Tint" lever does, change it while the photo is in B&W.
Hope this helps. Happy shooting!