Vega Scale Question - static mapping

[dandcp]

I apologize for the simplicity of this question, but I simply cannot figure it out from the Vega documentation and I suspect it's a simple answer.

I have a scatter chart that I've created and one of the things I do is color the bubbles based on a risk score (1 - 10). It works fine with a linear scale setup using a 3 color range. However, the issue is the scale becomes dynamic. For example if I have 10 items on the chart and they have values 1 - 10 then my items that have 1 will be red, my items that have 5 are yellow, and my items that are 10 are green (and shades in between). However, if I filter and only have 5 items (for example) and of the 5 the lowest score is a 6, then the 6 becomes red, and so on.

In short, I want to set a static scale that simply marks the bubbles as red if they are at the lower end of the scale, yellow if they are in the middle and green if they are at the top.

I think I can do this with a bin or an array, but I simply cannot figure out the syntax or if I'm looking at the wrong options. I have tried just about every "type" of scale to see the differences and can't seem to figure it out.

Any help would be appreciated.

[aaron-nimocks]

This is hard to visualize. Could you post your specification?

[aaron-nimocks]

Have you tried the redyellowgreen scale?

    {
      "name": "color",
      "type": "ordinal",
      "range": {"scheme": "redyellowgreen"},
      "domain": ............
    }