Pinhole diameter is based on focal length of camera. The finished pinhole can be measured using a flatbed scanner or buying a pre-made pinhole for your camera focal length.
Gap between pinhole and film is called the focal length.
Not sure about color filters with pinhole photo's but I have used B&W filters with my pinhole cameras and they work.
F/stop is pinhole size divided by focal length or visa versa.
1.23mm is 1.23mm
1.23cm is 12mm give or take.
Here is a great link. The program can be downloaded and it will tell you everything you need to know about what focal length and pinhole size to use plus f/stop size and eposure times-

Do you have any pre-made pinholes? What size camera are you thinking of building? Please feel free to contact me with any questions you might have.
Arthur, NYC