More fixes:

* Fill brush did not do proper srgb conversion for byte images (reported
by Sebastian Koenig, thanks!)
* Color sampling for palettes did not refresh the toolbar.

source/blender/editors/sculpt_paint/paint_image.c

@@ -1309,6 +1309,7 @@ static int sample_color_modal(bContext *C, wmOperator *op, const wmEvent *event)
 					data->sample_palette = true;
 					sample_color_update_header(data, C);
 				}
+				WM_event_add_notifier(C, NC_BRUSH | NA_EDITED, brush);
 			}
 			break;
 	}

source/blender/editors/sculpt_paint/paint_image_2d.c

@@ -1619,6 +1619,7 @@ void paint_2d_gradient_fill(
 				}
 
 				do_colorband(br->gradient, f, color_f);
+				linearrgb_to_srgb_v3_v3(color_f, color_f);
 				rgba_float_to_uchar((unsigned char *)&color_b, color_f);
 				((unsigned char *)&color_b)[3] *= br->alpha;
 				IMB_blend_color_byte((unsigned char *)(ibuf->rect + y_px * ibuf->x + x_px),

source/blender/editors/sculpt_paint/paint_image_proj.c

@@ -4104,6 +4104,7 @@ static void *do_projectpaint_thread(void *ph_v)
 							                      color_f, ps->blend);
 						}
 						else {
+							linearrgb_to_srgb_v3_v3(color_f, color_f);
 							rgba_float_to_uchar(projPixel->newColor.ch, color_f);
 							IMB_blend_color_byte(projPixel->pixel.ch_pt,  projPixel->origColor.ch_pt,
 							                     projPixel->newColor.ch, ps->blend);