patch 7.4.1552
Problem:    ":colorscheme" does not use 'packpath'.
Solution:   Also use in "start" and "opt" directories in 'packpath'.
diff --git a/src/syntax.c b/src/syntax.c
index ac80ab4..7d2233a 100644
--- a/src/syntax.c
+++ b/src/syntax.c
@@ -4813,7 +4813,7 @@
     prev_toplvl_grp = curwin->w_s->b_syn_topgrp;
     curwin->w_s->b_syn_topgrp = sgl_id;
     if (source ? do_source(eap->arg, FALSE, DOSO_NONE) == FAIL
-				: source_runtime(eap->arg, TRUE) == FAIL)
+				: source_runtime(eap->arg, DIP_ALL) == FAIL)
 	EMSG2(_(e_notopen), eap->arg);
     curwin->w_s->b_syn_topgrp = prev_toplvl_grp;
     current_syn_inc_tag = prev_syn_inc_tag;
@@ -7075,7 +7075,7 @@
 	else
 	{
 	    ++recursive;
-	    (void)source_runtime((char_u *)"syntax/syncolor.vim", TRUE);
+	    (void)source_runtime((char_u *)"syntax/syncolor.vim", DIP_ALL);
 	    --recursive;
 	}
     }
@@ -7104,7 +7104,7 @@
     if (buf != NULL)
     {
 	sprintf((char *)buf, "colors/%s.vim", name);
-	retval = source_runtime(buf, FALSE);
+	retval = source_runtime(buf, DIP_START + DIP_OPT);
 	vim_free(buf);
 #ifdef FEAT_AUTOCMD
 	apply_autocmds(EVENT_COLORSCHEME, name, curbuf->b_fname, FALSE, curbuf);