I spend quite a bit of time selecting and fine-tuning symbolization options for layers in web maps. The palette color picker in the "classic" Map Viewer saves me gobs of time. A color I pick there, often with transparency adjustments. That makes it quick and simple to set an appropriate color. But a BIG side benefit is that this approach allows me to assure that a color I use in one map or app can easily and quickly and confidently be "reused" to provide consistent color use across use cases. It thus sets up the ability to "enforce" standards for a set of maps and apps. When I go to a new map with a layer that I want to "reuse" a color, I can go to the palette and quickly pick, say, the magenta in the 3rd row in the last column. Choosing from the palette also sets--and continually reinforces--a spatial and visual "muscle memory" for often-used colors. Overall, this leads to clarity for users of your information products.
With the new Map Viewer, you are faced with having to always use slider bars, or remember and type in hexadecimal codes, constantly referring back to another map or layer to make sure you have the color right. It's tedious and frustrating. Picking from a palette is SO much easier, faster and repeatable. PLEASE add the palette to the new Map Viewer. Thanks.