diff --git a/src/monettheme.h b/src/monettheme.h
new file mode 100644
index 0000000..60a2a74
--- /dev/null
+++ b/src/monettheme.h
@@ -0,0 +1,46 @@
+#pragma once
+
+#include <monet/monet.h>
+
+#include "fcitx-utils/color.h"
+
+namespace fcitx::m3ui {
+
+// The colours of the candidate window that follow the desktop, taken from a
+// libmonet scheme. Only colours are decided here, the radii and the spacing stay
+// with the theme file.
+struct MonetColors {
+    Color surface;               // the panel
+    Color outline;               // its border
+    Color highlightFill;         // the pill behind the current candidate
+    Color normal;                // candidate text and the typed pinyin
+    Color highlight;             // the part of the typed pinyin being converted
+    Color highlightBackground;
+    Color highlightCandidate;    // text on the pill
+    Color candidateLabel;        // the number in front of a candidate
+    Color highlightCandidateLabel;
+    Color candidateComment;
+    Color highlightCandidateComment;
+};
+
+inline Color toColor(monet::Rgb c, int alpha = 255) {
+    return Color(c.r, c.g, c.b, static_cast<unsigned short>(alpha));
+}
+
+inline MonetColors mapScheme(const monet::Scheme &s) {
+    MonetColors c;
+    c.surface = toColor(s.surfaceContainer, 245);
+    c.outline = toColor(s.outlineVariant);
+    c.highlightFill = toColor(s.primaryContainer);
+    c.normal = toColor(s.onSurface);
+    c.highlight = toColor(s.primary);
+    c.highlightBackground = toColor(s.primaryContainer);
+    c.highlightCandidate = toColor(s.onPrimaryContainer);
+    c.candidateLabel = toColor(s.onSurfaceVariant);
+    c.highlightCandidateLabel = toColor(s.onPrimaryContainer);
+    c.candidateComment = toColor(s.onSurfaceVariant);
+    c.highlightCandidateComment = toColor(s.onPrimaryContainer);
+    return c;
+}
+
+} // namespace fcitx::m3ui
diff --git a/tests/monettheme_test.cpp b/tests/monettheme_test.cpp
new file mode 100644
index 0000000..4af4443
--- /dev/null
+++ b/tests/monettheme_test.cpp
@@ -0,0 +1,62 @@
+// The candidate window colours taken from a libmonet scheme must stay readable
+// for any seed, in both modes.
+//   g++ -std=c++20 -Isrc -I<libmonet>/include tests/monettheme_test.cpp
+//   (add the flags from: pkg-config --cflags --libs Fcitx5Utils)
+#include <cmath>
+#include <cstdio>
+
+#include "monettheme.h"
+
+using namespace fcitx::m3ui;
+
+static int failures = 0;
+#define CHECK_MSG(cond, ...)                                                       \
+    do {                                                                           \
+        if (!(cond)) {                                                             \
+            std::printf("FAIL line %d: %s  ", __LINE__, #cond);                    \
+            std::printf(__VA_ARGS__);                                              \
+            std::printf("\n");                                                     \
+            failures++;                                                            \
+        }                                                                          \
+    } while (0)
+
+static monet::Rgb rgb(const fcitx::Color &c) {
+    return {static_cast<std::uint8_t>(std::lround(c.redF() * 255)), static_cast<std::uint8_t>(std::lround(c.greenF() * 255)),
+            static_cast<std::uint8_t>(std::lround(c.blueF() * 255))};
+}
+
+int main() {
+    unsigned state = 4242;
+    auto next = [&] { state = state * 1664525u + 1013904223u; return static_cast<std::uint8_t>(state >> 24); };
+    std::vector<monet::Rgb> seeds = {{61, 174, 233}, {255, 176, 201}, {0, 0, 0}, {255, 255, 255}, {128, 128, 128},
+                                     {255, 0, 0},    {0, 255, 0},     {0, 0, 255}, {255, 255, 0}, {0x67, 0x50, 0xA4}};
+    for (int i = 0; i < 300; i++) seeds.push_back({next(), next(), next()});
+    for (auto seed : seeds) {
+        for (auto mode : {monet::Mode::Light, monet::Mode::Dark}) {
+            const MonetColors c = mapScheme(monet::generate(seed, mode));
+            const char *m = mode == monet::Mode::Dark ? "dark" : "light";
+            const auto surface = rgb(c.surface), fill = rgb(c.highlightFill);
+            auto pair = [&](const char *name, monet::Rgb bg, const fcitx::Color &fg, double min) {
+                CHECK_MSG(monet::contrast(bg, rgb(fg)) >= min, "%s %s, seed %s: %.2f < %.1f", m, name, monet::hex(seed).c_str(),
+                          monet::contrast(bg, rgb(fg)), min);
+            };
+            pair("candidate text", surface, c.normal, 7.0);
+            pair("candidate number", surface, c.candidateLabel, 4.5);
+            pair("candidate comment", surface, c.candidateComment, 4.5);
+            pair("typed pinyin being converted", surface, c.highlight, 4.5);
+            pair("text on the current candidate", fill, c.highlightCandidate, 7.0);
+            pair("number on the current candidate", fill, c.highlightCandidateLabel, 7.0);
+            pair("comment on the current candidate", fill, c.highlightCandidateComment, 7.0);
+            // the panel border can be seen against the panel
+            CHECK_MSG(monet::contrast(surface, rgb(c.outline)) >= 1.1, "%s border of seed %s", m, monet::hex(seed).c_str());
+            // the pill can be told apart from the panel, by tone since a container is only a few tones off the surface
+            CHECK_MSG(std::fabs(monet::toneOf(fill) - monet::toneOf(surface)) >= 3.0, "%s pill of seed %s: tones %.1f and %.1f", m,
+                      monet::hex(seed).c_str(), monet::toneOf(fill), monet::toneOf(surface));
+            CHECK_MSG(c.surface.alpha() == 245 && c.normal.alpha() == 255 && c.highlightFill.alpha() == 255, "%s alpha of seed %s", m, monet::hex(seed).c_str());
+            // dark panel in dark mode, light panel in light mode
+            CHECK_MSG((monet::toneOf(surface) < 50) == (mode == monet::Mode::Dark), "%s panel tone of seed %s", m, monet::hex(seed).c_str());
+        }
+    }
+    std::printf(failures ? "%d check(s) failed\n" : "monettheme: all checks passed\n", failures);
+    return failures ? 1 : 0;
+}