Windows utility that picks an RGB color, returning it's hex representation

pick.c

#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <windows.h>

// cc -Wall -O2 -o pick.exe pick.c -lcomdlg32

COLORREF fromhexstr(const char *hex)
{
    COLORREF color = 0;
    int i = 4, it = 0;

    const char *p = hex + 1;

    if (!*hex || *hex != '#')
        return 0;

    while (*p && it < 6) {
        if (*p >= '0' && *p <= '9') {
            color |= (*p - '0') << i;
            goto next;
        }

        if (*p >= 'a' && *p <= 'f') {
            color |= (*p - 'a' + 10) << i;
            goto next;
        }

        if (*p >= 'A' && *p <= 'F') {
            color |= (*p - 'A' + 10) << i;
            goto next;
        }

        return 0;
next:
        i = (it & 1) ? i + 12 : i - 4;
        it++;
        p++;
    }

    return it < 6 ? 0 : color;
}

COLORREF pick_color(COLORREF selcolor, HWND owner)
{
    CHOOSECOLOR color;
    COLORREF ccref[16];

    memset(&color, 0, sizeof(color));
    memset(ccref, 0, sizeof(ccref));

    color.lStructSize = sizeof(CHOOSECOLOR);
    color.hwndOwner = owner;
    color.lpCustColors = ccref;
    color.rgbResult = selcolor;
    color.Flags = CC_RGBINIT|CC_FULLOPEN;

    if (ChooseColor(&color))
        selcolor = color.rgbResult;

    return selcolor;
}  

int main(int argc, char *argv[])
{
    COLORREF color = 0x808080;
    HWND desk = GetDesktopWindow();

    if (argc > 1)
        color = fromhexstr(argv[1]);
    
    color = pick_color(color, desk);

    uint8_t r = color & 0xff;
    uint8_t g = (color & 0xff00) >> 8;
    uint8_t b = (color & 0xff0000) >> 16;

    printf("#%02x%02x%02x\n", r, g, b);

    return 0;
}