Set alpha to 1.0 in all the post shaders. Not that it should be required, but definitely recommended.

assets/shaders/4xhqglsl.fsh

@@ -69,7 +69,8 @@ void main()
   w4 = (i4.r+i4.g+i4.b+lc)*0.2; 
   w4 = clamp(k*dot(abs(c-i4),dt)/w4+mx,min_w,max_w);
 
-  gl_FragColor.xyz = w1*i1 + w2*i2 + w3*i3 + w4*i4 + (1.0-w1-w2-w3-w4)*c;
+  gl_FragColor.rgb = w1*i1 + w2*i2 + w3*i3 + w4*i4 + (1.0-w1-w2-w3-w4)*c;
+  gl_FragColor.a = 1.0;
 }
 
 

assets/shaders/aacolor.fsh

@@ -64,5 +64,6 @@ void main()
   color.g = pow(color.g+0.001,a);
   color.b = pow(color.b+0.001,a);
 
-  gl_FragColor.xyz = contrast4(x)*normalize(color*c_ch)*b;
+  gl_FragColor.rgb = contrast4(x)*normalize(color*c_ch)*b;
+  gl_FragColor.a = 1.0;
 }

assets/shaders/cartoon.fsh

@@ -47,5 +47,6 @@ void main()
   c11 = 4.0*normalize(c11); 
   vec3 frct = fract(c11); frct*=frct;
   c11 = floor(c11)+ 0.05*dt + frct*frct;
-  gl_FragColor.xyz = 0.25*lc*(1.1-d*sqrt(d))*c11;
+  gl_FragColor.rgb = 0.25*lc*(1.1-d*sqrt(d))*c11;
+  gl_FragColor.a = 1.0;
 }

assets/shaders/natural.fsh

@@ -53,6 +53,6 @@ c1=RGBtoYIQ*c0;
 
 c1=vec3(pow(c1.x,val00.x),c1.yz*val00.yz);
 
-gl_FragColor.xyz=YIQtoRGB*c1;
-
+gl_FragColor.rgb=YIQtoRGB*c1;
+gl_FragColor.a = 1.0;
 }