Most plants have a very strict dress code, donning the same colors and style every year. When colors vary, the plant is simply named something else, or it indicates that there is a problem.
Botanically, plant colors are fascinating to me. We all learn in science class that plants get their green color from chlorophyll in the leaves, and the plant uses the chlorophyll to photosynthesize and make food. So, when a plant has purple leaves, how does it eat?
The simple answer is that plants also contain two other leaf color pigments: carotenoids and anthocyanins. Various combinations of these three pigments in plant leaves gives them their seasonal dress colors.
Think about the colors of the rainbow. White sunlight includes all colors of the rainbow: red, orange, yellow, green, blue, indigo, and violet. Red, orange, and yellow make up the hotter, red end of the spectrum; while blue, indigo and violet make up the cooler, blue portion. Carotenoids give a plant its red colors, chlorophyll shows up green, and anthocyanin is blue.
When a plant gathers energy from the sun, it only absorbs the sun's colors that it doesn't already have. Since green plants have primarily green (chlorophyll) pigment, they only absorb the red and blue light from the sun. The leaf then reflects its green color, which is what we see.
Similarly, plants with primarily red (carotenoid) pigments absorb green and blue light rays, making their leaves appear yellow, red, or orange. Carotenoid pigments give carrots their orange color, and variegated plants their yellow color.
Those with high amounts of blue (anthocyanin) pigments, absorb red and blue light rays, making their leaves appear blue, purple, or indigo. This is the pigment we see in red apple skin and purple grapes.
Obviously, plant botany is much more complicated than this; but, I hope this helps start to explain plant colors.
Sometimes I think I'd like to be more plant-like and know exactly what I'm wearing every morning. Like Johnny Cash who only wore black, clothes shopping would be much easier (and maybe even cheaper). Still, I'd probably miss the fun and pretty variety that colors provide.