Found the problem. The skin's own CSS has a color for button, but it's not limited to the skin's own buttons. It's cascading down to the widget's button. Might be very tricky to correct the skin so that it's not generating CSS that spills over like this.
Adding this to Projector > Advanced > Custom code > CSS will, I believe, fix the problem:
Thanks for your reply - Out of curiosity I put your screen shot under a magnifying glass and believe it or not the "Post Comment" text IS there but its the same off color white as the text I am using in my album.