Only use Atop blend mode for faint text. It breaks subpixel antialiasing

sources/iTermTextDrawingHelper.m

@@ -1217,7 +1217,9 @@ typedef struct iTermTextColorContext {
     size_t length = numCodes;
     [self selectFont:font inContext:ctx];
     CGContextSetFillColorSpace(ctx, CGColorGetColorSpace(color));
-    CGContextSetBlendMode(ctx, kCGBlendModeSourceAtop);
+    if (CGColorGetAlpha(color) < 1) {
+        CGContextSetBlendMode(ctx, kCGBlendModeSourceAtop);
+    }
     CGContextSetFillColor(ctx, components);
     double y = point.y + _cellSize.height + _baselineOffset;
@@ -1257,6 +1259,9 @@ typedef struct iTermTextColorContext {
     if (useThinStrokes) {
         CGContextSetFontSmoothingStyle(ctx, savedFontSmoothingStyle);
     }
+    if (CGColorGetAlpha(color) < 1) {
+        CGContextSetBlendMode(ctx, kCGBlendModeNormal);
+    }
     return length;
 }