Index: source/blender/gpu/intern/gpu_extensions.c
===================================================================
--- source/blender/gpu/intern/gpu_extensions.c	(revision 28151)
+++ source/blender/gpu/intern/gpu_extensions.c	(working copy)
@@ -71,7 +71,7 @@
 	GLuint currentfb;
 	int glslsupport;
 	int extdisabled;
-	int color24bit;
+	int screenDepth;
 	GPUDeviceType device;
 	GPUOSType os;
 	GPUDriverType driver;
@@ -109,8 +109,10 @@
 	if (!GLEW_ARB_fragment_shader) GG.glslsupport = 0;
 
 	glGetIntegerv(GL_RED_BITS, &bits);
-	GG.color24bit = (bits >= 8);
-
+    /* three colour channels all at the same depth seems feesible
+    or should we get all three to be exact?? */
+    GG.screenDepth = bits * 3;
+    
 	vendor = (const char*)glGetString(GL_VENDOR);
 	renderer = (const char*)glGetString(GL_RENDERER);
 
@@ -177,9 +179,14 @@
 
 int GPU_24bit_color_support()
 {
-	return GG.color24bit;
+	return GG.screenDepth==24;
 }
 
+int GPU_screen_depth()
+{
+    return GG.screenDepth;
+}
+
 int GPU_print_error(char *str)
 {
 	GLenum errCode;
Index: source/blender/gpu/GPU_extensions.h
===================================================================
--- source/blender/gpu/GPU_extensions.h	(revision 28151)
+++ source/blender/gpu/GPU_extensions.h	(working copy)
@@ -62,6 +62,7 @@
 int GPU_glsl_support(void);
 int GPU_non_power_of_two_support(void);
 int GPU_24bit_color_support(void);
+int GPU_screen_depth(void);
 
 /* GPU Types */
 
Index: source/blender/windowmanager/intern/wm_subwindow.c
===================================================================
--- source/blender/windowmanager/intern/wm_subwindow.c	(revision 28151)
+++ source/blender/windowmanager/intern/wm_subwindow.c	(working copy)
@@ -49,6 +49,13 @@
 #include "wm_subwindow.h"
 #include "wm_window.h"
 
+/*  the following prototypes are added as extern only to prevent changing
+    header search paths - this should probably be done and the following used
+    to replace these two prototypes.
+    #include "GPU_extensions.h" */
+extern void GPU_extensions_init(void); /* call this before running any of the functions below */
+extern int GPU_screen_depth(void);
+
 /* wmSubWindow stored in wmWindow... but not exposed outside this C file */
 /* it seems a bit redundant (area regions can store it too, but we keep it
    because we can store all kind of future opengl fanciness here */
@@ -306,15 +313,17 @@
 	static int mainwin_color_depth= 0;	
 	
 	if(mainwin_color_depth==0) {
-		GLint r, g, b;
+        /*GPU_extensions_init(); 
+        comments say this should be called before the following 
+        but it causes a crash if called here - second glewInit() call maybe??
+        I guess we can safely assume that at this point the GPUGlobals struct 
+        is initialised and available */
+		mainwin_color_depth = GPU_screen_depth();
 		
-		glGetIntegerv(GL_RED_BITS, &r);
-		glGetIntegerv(GL_GREEN_BITS, &g);
-		glGetIntegerv(GL_BLUE_BITS, &b);
-		
-		mainwin_color_depth= r + g + b;
 		if(G.f & G_DEBUG) {
-			printf("Color depth r %d g %d b %d\n", (int)r, (int)g, (int)b);
+		    GLint r;
+			printf("Color depth %d\n", mainwin_color_depth);
+			/* not sure if GL_AUX_BUFFERS will work here either */
 			glGetIntegerv(GL_AUX_BUFFERS, &r);
 			printf("Aux buffers: %d\n", (int)r);
 		}