To use this simply create a new bookmark and copy past the code in the url field. Then you only need to click on the bookmark to execute the script.
javascript: (function () {
if (document.children[0].style['filter']) {
document.children[0].style['filter'] = ''
} else {
document.children[0].style['filter'] = 'invert(100%) hue-rotate(180deg)'
}
})()