DM Mystery, show crits or fumbles

I use the double square brackets i.e.  [[ [[ die type +/- modifiers ]] ]] to hide the math from my players, but I would like to know when I roll a Natural 1 or 20. Is there some way to do this?

Not that I can think of, without access to Roll20 Mod Scripts (Pro Subscriber Perk).  

Die rolls should be color coded, red if it rolls the lowest value, green if it rolls the highest, and you can hover over the result to see the individual rolls. It can get confusing if there are multiple dice (and it uses blue I think if there are a mix of highest and lowest) plus there is also an option to roll the 3D dice on the screen, although I believe that is a player setting and some folks have had problems with it lagging the graphics.

MysterX, Rich is using the trick where you wrap an inline roll in an inline roll to end up with just a number: That prevents seeing the roll or the adjustments, but also obscures the crit/failure color:

Could do it with the reusisng rolls trick: [[[[[[d20]]+9]]]] $[[0]] Just wrap the d20 (or whatever your die roll is) in another set of brackets. Then you can reference that roll with $[[0]] (assuming it's the first term. Gives output like: Rainbow Encoder has a very complex forum thread on more complex ways to use this basic technique, including some work arounds that let you do actual operations with the reused roll. I don't fully understand those workarounds, or I'd show you how to use them here.

If you don't mind your players also knowing if you nat 1/20 this macro will show your crits/fails/other as 20/1/0 with colour coding and without leaking actual values otherwise. [[1-1d[[({ 10,[[ [[ 1d20 +(?{Mod|0})]] ]]-(?{Mod})}>20f1+3)%3-1]]cs0*19+19]] &{template:default} {{Roll=$[[1]]}} {{Crit=$[[3]]}} It works by by subtracting the original modifier to get to the raw d20 value converting that with target number syntax then some parser halting trickery (see link in Scott's post above) to get the colour coding and final values. In this instance the really difficult stuff isn't needed.