The thing to remember is that bright does not mean it will be seen. What you need is contrast.
Silver is generally bad, as is that preserve of light aircraft - white. These provide little or no contrast against most sky colours.
Black on the other hand does show up very well (yes I know the CIA had this strange idea of painting all their spy aircraft black, why do you think they get shot down?).
Try getting a large sheet of paper and paint it starting white at one end, going through shades of grey to blues at the other. (or a large sky poster). Then cut out some silhouettes of your aircraft and colour these in. Place on different areas of your "sky" and see which ones show up best. Oh, and when doing this, squint. Squinting puts it all out of focus and highlights the contrast.
Colours that will probably work well are black, dark reds and oranges, dark blues, and greens. Neutral and light colours will probably work less well.