Colors of the lua gui.* API are incorrect

[Perdu]

(Continuation of the Discord discussion)

Colors printed by the different gui.* functions of the Lua API seem to me to be incorrect compared to their provided value.

I initialy spotted that by trying to draw a rectangle the same color as this game's wall (0x797988 color), but the following code draw a incorrect color (0xb7b7c1): gui.rectangle(410, 577, 380, 22, 1, 0xff797988, 1) (bottom right rectangle)

To investigate further, I made two scripts: one that would draw all greyscale colors from 0 to 255 in python using matplotlib, one with libTAS. As you can see, libTAS clearly draws a wider ranger of lighter colors (python is left, libTAS is right):

My guess is an incorrect decimal - hexadecimal conversion somewhere.

For completeness, Python code:

import numpy as np
import matplotlib.pyplot as plt

band_height = 4
width = 800

height = 256 * band_height
img = np.zeros((height, width, 3), dtype=np.uint8)

for i in range(256):
    img[i*band_height:(i+1)*band_height, :, :] = i

plt.figure(figsize=(8, 10))
plt.imshow(img)
plt.axis("off")
plt.title("Grayscale bands (0–255)")
plt.show()

libTAS lua code:

function onPaint()
    local bandHeight = 4
    local screenWidth = 100

    for i = 0, 255 do
        local grey = i
        local color =
            0xFF000000 |      -- alpha = 255
            (grey << 16) |    -- red
            (grey << 8)  |    -- green
            grey              -- blue

        local y = 50 + i * bandHeight / 2

        for dy = 0, bandHeight do
            gui.line(100, y, 100 + screenWidth, y + dy, color)
        end
    end
end