Three colours, with the arithmetic left in.

25% blue over a warm background

Foreground

#2468AC = (36, 104, 172)

Background

#F0E0C0 = (240, 224, 192)

Opacity

25% = 1/4

Red: (36 + 3 × 240) / 4 = 189.
Green: (104 + 3 × 224) / 4 = 194.
Blue: (172 + 3 × 192) / 4 = 187.

All channels are integers already. The exported value is #BDC2BB, or rgb(189, 194, 187). This is the calculator's reset example.

40% rust over a dark blue

Foreground

#CC6633 = (204, 102, 51)

Background

#204060 = (32, 64, 96)

Opacity

40% = 2/5

Red: (2 × 204 + 3 × 32) / 5 = 504/5 = 100.8.
Green: (2 × 102 + 3 × 64) / 5 = 396/5 = 79.2.
Blue: (2 × 51 + 3 × 96) / 5 = 78.

The exact channels are not all integers. Nearest-integer export gives (101, 79, 78), which serialises as #654F4E. The displayed token is the rounded result; the fractions remain useful when checking the calculation.

The exact half: white over black

Foreground #FFFFFF, background #000000, opacity 50%. Every channel becomes (255 + 0) / 2 = 255/2 = 127.5. An exact half rounds upward under this tool's chosen export rule, so every 8-bit channel is 128.

The exported colour is #808080. This is the midpoint of encoded channel numbers. It is not a linear-light midpoint or a universal browser-pixel promise.