Revert "Prevent transparent black"

This reverts commit 486ccfa5f3.

app/src/main/java/eu/faircode/email/HtmlHelper.java

@@ -2084,7 +2084,7 @@ public class HtmlHelper {
     static String encodeWebColor(int color) {
         int alpha = Color.alpha(color);
         int rgb = 0xFFFFFF & color;
-        if (alpha == 255 || color == 0)
+        if (alpha == 255)
             return String.format("#%06X", rgb);
         else
             return String.format("#%06X%02X", rgb, alpha);