Also proposed on Hookshot: simonwjackson/Hookshot feat-colour-filter.
Cherry-picked source: 89c5a69, e4f5407.
Resolve rename/context conflicts without changing feature behaviour.
Keep measured configurations in the PR description, not the shared table.

Assisted-by: OpenAI GPT-6 Astra
Co-Authored-By: OpenAI GPT-6 Astra <[email protected]>

@@ -87,0 +87,4 @@
+// Correction follows scaling/sharpening, before Expanded HDR encoding and host overlays.
+vec3 accessible(vec3 c) {
+    // Keep the old shader path exact with neutral settings, even while scaling is active.
+    if (pc.colour[0] == 1.0 && pc.colour[4] == 1.0 && pc.colour[8] == 1.0) return c;

@@ -55,2 +55,4 @@
    90, 120, 144, 165, 240, 6 Uncapped; a change applies in play) */
 enum { HOS_OPT_FPS_CAP = 53 };
+/* Graphics: live colour correction, 0 Off, 1 Protanopia, 2 Deuteranopia, 3 Tritanopia. */
+enum { HOS_OPT_COLOUR_FILTER = 56 };

@@ -34,6 +34,7 @@
 #include "shaders/fg_luma_comp_spv.h"
 #include "shaders/fg_median_comp_spv.h"
 #include "shaders/fg_scale_comp_spv.h"
+#include "colour_filter.h"

@@ -595,2 +596,3 @@
     const WideSides wide = wide_now.load(std::memory_order_relaxed);   // (wide_sides_tick, each present)
-    if (!opts.upscale && !opts.sharpness && !wide.side) return VK_NULL_HANDLE;
+    // Native HDR supplies PQ codes, not sRGB. Leave that path unchanged, including its SDR fallback.
+    const int colour = opts.hdr == 2 ? 0 : opts.colour_filter;

@@ -1241,6 +1245,8 @@ Row rows[] = {
      "tone mapper, the same mid grey with highlights that roll off into the peak and keep their colour.",
      nullptr, false, true},
     {TAB_GRAPHICS, "Detail", nullptr, 0, 0, 0, nullptr, nullptr, nullptr, false, true, -1, true},
+    {TAB_GRAPHICS, "Colour filter", &opts.colour_filter, 0, 3, 1, tx_colour_filter,

@@ -0,0 +8,4 @@
+def main():
+    p=argparse.ArgumentParser();p.add_argument('--cxx',default='clang++');a=p.parse_args()
+    header = (ROOT / 'gpu/vk/vk_menu.h').read_text()
+    menu = (ROOT / 'gpu/vk/vk_menu.cpp').read_text()