Why have you chosen Feng shui?

I think you are confusing yourself for nothing. I have nothing against it, but this should not be this difficult or confusing.

Your front door is the one where people who don't know you well arrive and ring the doorbell. Paint it a color you like that complements the rest of your house.

In Feng Shui, it is important to pair the front door color with the color of your house, in order to achieve a nourishing cycle.

Would you mind posting a photo of your house?

What is the type of landscape (and the region) you are in (dry, desert, cold, rainy, flat, windy?), in order to know what color would be best suited for the doors.

If say, your house is painted dark blue, which is a Water color, then there is no need to paint your doors dark blue as well. Especially if there is already a stream of water in your backyard... This makes me think you do not live in a draught area either.

PS: In FS, blue is not generally considered a Water color, except Dark Blue. Blue is generally Wood.

The idea is to achieve a balance of the 5 elements. The other goal of renovating a main entrance is to attract more "Chi" (or energy) into the home. If all the elements are Water, then the energy will probably not be vibrant enough (and too emotional).