MED posted:... but here is a possible way to control current ramp through LEDs.
There is reason to use a microcontroller/Arduino as GRJ suggests for fade-in/fade-out. The brightness change for a flashing incandescent bulb is not correctly modeled by the ramp-up/ramp-down of a resistor-capacitor. Agreed, we're talking hobby-grade and most guys would be satisfied with any fade effect. The microcontroller would permit a more prototypical fade-in/fade-out effect at no extra cost once it's put in place (i.e., "just" a few more lines of code! ).