make sure drop shadows don't polute the color context (scp-fs2open#6689)

Author: MjnMixael

code/hud/hud.cpp

@@ -915,9 +915,10 @@ void HudGauge::renderString(int x, int y, const char *str, float scale, bool con
 	}
 
 	if (HUD_shadows) {
+		color cur = gr_screen.current_color;
 		gr_set_color_fast(&Color_black);
 		gr_string(x + nx + 1, y + ny + 1, str, resize, scale);
-		gr_set_color_fast(&gauge_color);
+		gr_set_color_fast(&cur);
 	}
 
 	gr_string(x + nx, y + ny, str, resize, scale);
@@ -951,16 +952,18 @@ void HudGauge::renderString(int x, int y, int gauge_id, const char *str, float s
 
 	if ( gauge_id > -2 ) {
 		if (HUD_shadows) {
+			color cur = gr_screen.current_color;
 			gr_set_color_fast(&Color_black);
 			emp_hud_string(x + nx + 1, y + ny + 1, gauge_id, str, resize, scale);
-			gr_set_color_fast(&gauge_color);
+			gr_set_color_fast(&cur);
 		}
 		emp_hud_string(x + nx, y + ny, gauge_id, str, resize, scale);
 	} else {
 		if (HUD_shadows) {
+			color cur = gr_screen.current_color;
 			gr_set_color_fast(&Color_black);
 			gr_string(x + nx + 1, y + ny + 1, str, resize, scale);
-			gr_set_color_fast(&gauge_color);
+			gr_set_color_fast(&cur);
 		}
 		gr_string(x + nx, y + ny, str, resize, scale);
 	}

code/hud/hudets.cpp

@@ -914,6 +914,7 @@ void HudGaugeEts::blitGauge(int index, int ix, int iy, float scale, bool config)
 
 	int x, y;
 	if (HUD_shadows) {
+		color cur = gr_screen.current_color;
 		// These act more as a backing black layer.
 
 		gr_set_color_fast(&Color_black);
@@ -930,7 +931,7 @@ void HudGaugeEts::blitGauge(int index, int ix, int iy, float scale, bool config)
 		renderBitmapEx(Ets_bar.first_frame, x, y, w, y + ETS_bar_h, 0, 0, scale, config);
 
 		if (!config) {
-			gr_set_color_fast(&gauge_color);
+			gr_set_color_fast(&cur);
 		} else {
 			setGaugeColor(HUD_C_NONE, config);
 		}

code/hud/hudreticle.cpp

@@ -329,12 +329,13 @@ void HudGaugeReticle::render(float  /*frametime*/, bool config)
 
 	if (fixed_reticle >= 0) {
 		if (HUD_shadows) {
+			color cur = gr_screen.current_color;
 			gr_set_color_fast(&Color_black);
 
 			// Render the shadow twice to increase visibility
 			renderBitmap(fixed_reticle, x + 1, y + 1, scale, config);
 			renderBitmap(fixed_reticle, x + 1, y + 1, scale, config);
-			gr_set_color_fast(&gauge_color);
+			gr_set_color_fast(&cur);
 		}
 
 		renderBitmap(fixed_reticle, x, y, scale, config);