For my third alien vegetation project, I thought that the Hive Mind might 'grow' some of its vital resources, such as metals. (Although they do have burrowing bugs…)
Plus I wanted to do this project on the cheap, and I had a spare spray-can of chrome silver hanging around.
What I learned was that if you paint a cotton pod silver, it turns into a light gray cotton pod. The metallic qualities are entirely lost on the cotton, though the leaves turn brightly silver.
And then the can clogged, just as I finished the first few pods. (Yes, it was an old, spare can of spray-paint.)
Looking through my miscellaneous cans of spray paint, I decided to continue the experiment – this time with copper paint.
Again, a similar result: the cotton turned dark brownish, while the leaves were darkly metallic. I sprayed the cotton pods three times, trying to get good coverage: top, bottom, then as-needed.
When I got the cotton pods to my painting table, I started by painting the leaves spring green, as I had for my original batch. I wanted them to look like living plants.
Then I touched up the cotton by brush. Despite my valiant efforts, the cotton needed a lot of touch up. Fortunately, I had some Antique Copper paint that was a good match for the spray paint. The spray paint seemed to form a primer coat of sorts for the cotton, even when the color hadn't taken. However, I still wasn't getting much of a metallic effect.
So I went back with a coat of a brighter metallic (actually, a bronze paint). Although I was brushing it on full-strength with a half-inch flat brush, the result looked like I had drybrushed it on, and I finally got a metallic effect. I'm guessing that I finally got the effect because I had layered enough paint onto the cotton.

Above, you can see a finished plant. I did not apply a seal coat, as I did not want to lose the metallic effect.

I did a batch of 16 plants, enough to make a large terrain item in Alien Squad Leader.

Above, you can see Giant Acid-Shooting Scorpions taking cover amid the copper plants. I had a lot of the single-ball cotton pods, so I used those exclusively for this batch.

Above, you can see the three varieties of alien plant I have painted so far: unripe, copper and sweet.