diff --git a/app/shaders/diptoblack.frag b/app/shaders/diptoblack.frag
index 30a9c918d..499b03b53 100644
--- a/app/shaders/diptoblack.frag
+++ b/app/shaders/diptoblack.frag
@@ -13,8 +13,9 @@ out vec4 frag_color;
 
 void main(void) {
     if (out_block_in_enabled && in_block_in_enabled) {
-        vec4 out_block_col = mix(texture(out_block_in, ove_texcoord), color_in, ove_tprog_out);
-        vec4 in_block_col = mix(texture(in_block_in, ove_texcoord), color_in, 1.0 - ove_tprog_in);
+        // mix(x, y , a): a(1-x) + b(x)
+        vec4 out_block_col = mix(color_in, texture(out_block_in, ove_texcoord),ove_tprog_out);
+        vec4 in_block_col = mix(color_in, texture(in_block_in, ove_texcoord), ove_tprog_in);
 
         frag_color = out_block_col + in_block_col;
     } else if (out_block_in_enabled) {