Found in the process of creating a test for  bug 806247  (https://crrev.com/c/1071126): when styling ::placeholder with a color, and also styling ::first-line with a color, the color that ::first-line was set to overrides the color that ::placeholder was set to.

A testcase for this issue is https://codepen.io/anon/pen/jxojMV.

This appears to work in Firefox 60, and Edge 17 (if a prefixed version of ::placeholder is used). Unclear about Safari.