As an artist you know there is no steadfast rule about how to determine colors for your paintings. Many times colors are determined by the mood of the artist, the colors of the intended space where the picture will be hung or the buyer’s preference. Background colors should enhance the positive space of a painting, not overwhelm the primary subject, the flower.
Look for a complementary color to the flower’s petals. Use a color wheel to figure out the best shades and hues to the subject’s primary color.
Paint the background a bold color that compliments the flower, but does not overpower it. Use the background to highlight the subject.
Pick the color of the flower’s petals and then lighten the hue. Paint the background a much lighter version of the flower’s petals to give the picture depth and dimension.
Stay within the color scheme of the subject. Tone the colors down; make them a bit dull or neutral so the background does not overshadow the flower.
Paint a realistic picture and use the colors of a natural background, blue for the sky, greens for the grass and black for dirt. If the picture is of a picked flower, use a muted color so the subject stands out.
Use your imagination. As an artist, you can create any look you want.