Colouring things

Once upon a time I worked up a spreadsheet where you could, for example, color the DOW.
I ran across that spreadsheet yesterday and was delighted by the pretty pictures is generated.
 >Huh? Color the DOW? Yeah. You download a bunch of data and generate a picture like Figure 1. It shows the weekly returns, week-by-week, over five years and the colours indicate how often they occur. >So? So I thought it'd be neat to download 10 years worth of weekly prices, calculate X = average return and Y = volatility, over N weeks, then colour the (X,Y) cells so see which occur most frequently. Figure 1
For example, Figure 2 looks at 10 years of weekly GE stock data and the average 20-week return (that's X) and volatility (that's Y):

Figure 2

>What are those numbers ... in the coloured cells?
They're the frequency with which that combination (X,Y) occurred.
For example, in the red cell it says 6.8%. That means ...
>That combination occurred 6.8% of the time?
Yes, how often ... during that particular 10-year time period.
>Is that useful? I mean, how often would I want to know how often ...?
Well, there are lots of things that can be calculated when the return and volatility are known, like the Sharpe Ratio.
So, if pick some risk-free rate, say Rf, and you know how often (X,Y) occurs, you also know how often (X -Rf) / Y occurs.
>I assume there's a ...