diff --git a/fw/Core/Src/main.c b/fw/Core/Src/main.c
index c184977..2bcd962 100644
--- a/fw/Core/Src/main.c
+++ b/fw/Core/Src/main.c
@@ -902,16 +902,28 @@ void CO2_to_color(uint16_t co2, uint16_t co2_limit_yellow, uint16_t co2_limit_re
 {
 	const uint16_t co2_limit_green = 400; /* fresh air, lowest possible value */
 
-	uint32_t co2_full_span;
+	uint32_t co2_interval_length;
+	uint32_t co2_lower_limit;
 	uint32_t intensity;
+	uint32_t intensity_offset;
 
 	if (co2 < co2_limit_green) {
 		rgbled_set_color(RGBLED_GREEN);
 	} else if (co2 > co2_limit_red) {
 		rgbled_set_color(RGBLED_RED);
 	} else {
-		co2_full_span = co2_limit_red - co2_limit_green;
-		intensity = (co2 - co2_limit_green) * 255 / co2_full_span;
+		if (co2 < co2_limit_yellow) {
+			/* first interval: from green to yellow (co2_alert_limit1) */
+			co2_interval_length = co2_limit_yellow - co2_limit_green;
+			co2_lower_limit = co2_limit_green;
+			intensity_offset = 0;
+		} else {
+			/* second interval: from yellow to red (co2_alert_limit2) */
+			co2_interval_length = co2_limit_red - co2_limit_yellow;
+			co2_lower_limit = co2_limit_yellow;
+			intensity_offset = 127;
+		}
+		intensity = (co2 - co2_lower_limit) * 128 / co2_interval_length + intensity_offset;
 		rgbled_set_color(intensity, 255 - intensity, 0);
 	}
 }