craftgrrl | Fabric Changes Colour with Heat?

I am having a strange problem. In altering a skirt, I've removed the lining (100% acetate). I want to iron out the few but stubborn wrinkles before sewing the fabric back on.
However...any time I touch it with a warm iron, it changes colour from the original olive to an alarming dark orange. Actually, it just becomes tinged with the orange but it gets worse with more heat. Oddly, the dark orange tinge seems to disappear and revert to the olive once the fabric is completely cool.
So here's the question: can I iron this fabric without permanently discolouring it? Yes, it seems to change right back to olive, but the fabric will now be on the outside of the skirt, so it's important that it look nice.
Anyone familiar with this odd quality of acetate? Will ironing it cause colour change, or make it less shiny/shimmery (i.e. more dull)?

Thanks!
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