After hitting the problem I asked to Claude and it confirmed that: > Text-based emojis (like 😀 🎨 🌟) are rendered as font glyphs by the operating system, not as images. CSS filters like grayscale work on the rendered pixels of HTML elements, but the OS renders emoji fonts in a way that bypasses these filters. Emoji rendering varies by platform: On macOS/iOS: Apple Color Emoji font On Windows: Segoe UI Emoji font On Android: Noto Color Emoji font These are system-level fonts that render with colors "baked in" at a layer that CSS filters can't reach. and then proposed some absurd solution, like converting emoji to images. So I immediately started ranting. Instead I just found out that the bug was on my side, ops. CSS are fine, at least in this case. Sorry! Instead LLMs are crappy, damn. (yes I double checked that I asked the right question, haha)