Definately prewash your red silk! Here's a story my friend Becca sent me about a red silk gown I made her...

"At lunchtime the heavens opened and we had some of that rain that's like having buckets of water thrown at you. I'm officially reporting that the red silk is not dyefast, but on the upside it is machine washable in cold water. I had to put it in the machine as the gravel paths at the castle were laid with something very like fullers earth that just caked over everything in the rain. The water soaked almost up to my waist, with gravel
splash right up to my chest. It was already soaking wet, so I thought what harm can a little more do.... I put the gown and 1.5 kilos of salt in the machine and it's pretty dyefast now too, so all's well that ends well! (tho I now have candystriped shifts with red armpits - nice!!)."

She did say that the red eventually washed out of the shifts.

Indeed you might want to consider only using the silk for the collar and cuffs, where they show when the gown is worn, and keeping a wool or fustian for the body and sleeves proper.

Entirely usual and seen in the Mss and the use of a different cloth for colars appars in many written sources from the Pastons to the Household accounts of Sir John Howard.