This time of year I hear a lot of people wondering what sort of fonts they should use for their boat name. 5 years ago about this time we had the same discussions. At that time we decided that the boat's name should be short, easily recognized, and easy to spell in phonetics. This shortened our name list considerably and Iris avoided being named "Queen Wilhelmina" although that is a perfectly lovely choice, if it works for you.
In any case this about font and colour, not names. Here are a couple of pics of Iris as she sits today. We are still prepping her for spring launch. She has a sort of boom tent over the cockpit since I have a few projects on the go up there. The reason for the pics though is so you can get a feel for what our lettering/font size looks like. If you are handy with graphics programs, feel free to overlay your boats name in whatever font you choose, and you will see what your name of choice looks like in your font of choice on a Catalina 25.
Font choices for boat names are pretty much unlimited. I have seen everything from scrawly little-kid writing to beautiful swirls and twirls in cursive writing to bold calligraphy. Our reasoning wiped most of these clear. We felt that it was important that another boat be able to see our name and hail us from afar, so we wanted a clear, simple font that anyone could read.
In the end we got what you see below. I believe the font is "Callibri" but I don't remember. For colour we went with a strong contrast to the hull colour, and we spaced the letters far enough apart that they could easily be read without blurring into each other. If I were to redo the lettering on iris, I might move the letters further apart to better define them from each other.
For scaling, the capital letter 'I' in each of these pictures is your best way to measure the height of the font. On the side of the boat, the 'I' is 12" high. On the transom, the 'I' is 7-1/2" high. If you dig around in your graphics software, you should be able to scale a photo to size, and that will allow you to judge the best height for your lettering (click on photos to open in full size).
Finally, some folks get all excited about applying the decals once they buy them. You can buy your name from about any vinyl graphics place, and there are many both online and brick-and-mortar shops that will make up the lettering for you. Look for signmakers, automobile graphics, and window decals in the yellow pages. The name will arrive on a sheet of paper. You position the name where you want it, and hold it in place with a couple pieces of masking tape, then peel off the backing, stick the letters where you want them, and smooth them out using a plastic spreader available in the fiberglass/bodywork section of an auto parts store for $2.
I have been told that it is best to wait for a calm day for this job. A breeze can blow the sticky letters after the backing paper is removed, causing the letters to stick to the boat or each other when you aren't prepared for it. This will result in some, erm, "customization" beyond what you intended.
Good luck, and happy naming!