Hi. I don't have a lot of experience with pressing, but I have some with drieds in general. I understand your feeling discouraged about doing work that will last a short time. These are some blooms in my experience that have held their color for several years: Cornflowers (Batchelor's Buttons) blue, red, and pink, Larkspur-darker blues/purples did better, pastel blues got dingy. Pink shades, light and dark, did well. Blue Pee Gee type hydrangeas, Pansies- darker blues/lavenders did best; orange shades also held their color. Red and pink carnations keep their colors for a very long time. Rudbeckia do fade after a year or so, but do so pretty evenly, so they may work for you. Zinnias, pinks & purples,
last a long time. Oranges & yellows fade for me, and whites look dirty. Reds turn brownish, but the color lasts. White Ammi stays white.
I hope someone with more experience will help you with more examples.

I'm not sure if it was this forum or possibly one of the craft forums, but there was a discussion about botanical prints of pressed material and how to preserve their color. It was suggested that a scanner or color copier could be used to copy the image onto high quality art paper. It sounded like a great idea to me.

I know it's not the same as having a picture using the real thing, but I've never done nor have I seen a dried flower picture that didn't lose its color, particularly if you use leaves, which seem to lose their green tones at a very fast rate.

kms