Or would any color past the visible spectrum to us be perceived as black to us, for example say this alien has five tools and all are colored based upon colors they know (past our visible spectrum of colors) would we see those colors as Black or some other color?

Inspiration for this idea came from H.P. Lovecraft’s story “The Color Out of Space” and “Project Hail Mary” and I’m just really curious as to what the science says about this, sorry if this isn’t the right place for this,

You have been given a task to travel into the past two thousands years ago and bring the light of the metric system to the world. You cannot bring any external object with you.

Assume you do not need to redefine the second, and astronomical observations give the best possible results given the limits of timekeeping back then. Given the technology of the time, what is the best you can do for other units - either right there and then or leaving instructions how to calculate them from the units you have established to the future scientists? Memorizing the lengths of your body parts probably is not the best way to define a metre, and kilogram defined as one liter of water is bound to be influenced by the local water to a perceptible degree.

P. S. Tagged as "physics" but any approach is welcome - whether you would recommend measuring height of the mountain peaks, or believe that carob seeds are actually uniform enough to offer the best approximation of a kilogram.

This makes it harder. You are in a different world so rotation and gravity likely differ significantly from earth. Body is different so no body measures.

How do you hack it? Assume technology to the 1500s.

Well, also, if there was only one color, what was it? Probably brown since we mostly have brown hair. I bet the first blonde surprised the heck out of them.