http://root.cern.ch/root/html/TColor.html
http://root.cern.ch/drupal/content/how-define-smooth-color-palette

Another example of ROOT pain – a ridiculous amount of code to set label size in pixels, and this has to be done for every label!
http://root.cern.ch/root/roottalk/roottalk97/1194.html

If I was aiming for a longer post I certainly would have mentioned ROOT’s PAW roots (hey, a pun, what a way to start!), but I don’t see how the history sheds any positive light. I’m sure there are reasons for most of the design choices in ROOT, but I really hope they are better than “this is the way PAW did it.” I can’t imagine a worse reason (well, beyond egregious ones like “I don’t know” or “we want to make this painful for you”). The age of ROOT might excuse it for some quirks like not using the STL, but regarding the issues I mentioned in this post I see no excuses. Switching the default background of pads to flat white will not break any code, in fact it could do nothing but spread goodness through the HEP community. Elliot says the default style is “okay for a computer screen” and I agree, but I don’t know anyone who actually prefers it to white in any output media. And, once you go to print the default style is absolutely terrible.

The issue of the default palette is similar. First of all, I don’t see how the default palette could be “the palette of 16 colors computers used about 20 years ago”. The default palette has 50 colors! Maybe this 16 color palette is some subset? For reference here are some 8-bit computer palettes In ROOT’s palette the first 8 colors are grays and at least the next 8 are reddish browns. The last 8 are fully saturated colors, but here the color red is repeated twice! (Note: the first 16 colors by color index makes a more plausible palette, they are mostly grays or saturated colors; but even here there are quirks, like the two whites, (1.0,1.0,1.0) and (0.999, 0.999, 0.999).) It’s certainly a mystery how this evolved out of a simpler primitive palette. Obviously the larger palette was chosen at some point, in which case the question remains, why these colors? A hint comes from the ROOT documentation where it says “the colors defined in [the default] palette are good for coloring pads, labels, and other graphic objects.” Does anyone actually use the palette for coloring pads? I’ve only been working in HEP for 5 years, but still, in all that time I have never seen any work that seemed to use the color palette as-is except in the case of a 2D histogram (and maybe for an array of stacked histograms, but usually this could just be a set of consecutive color indices). Notice also that the description of TColor::SetPalette() only mentions the 2D histogram example. The description even makes some erroneous claims about the palette colors; for example, palette colors 19 and 20 are distinctly green, not “brown” or “blueish.”

In addition, I hinted at a serious practical problem when making 2D histograms with the default palette. Even if you ignore the ugliness (maybe you even think it is beautiful), you can’t ignore the fact that colors are repeated, but in a an irregular way. You can see for yourself in the code, the red (index 2) is repeated near the end of the palette. Also, there are some brown colors which are very similar but occur in disjoint groups. This certainly aggravates the interpretation of the plots when using this palette. Finally, while I was poking around just now I noticed that the issue of repeated reds is not present in older versions of TStyle::SetPalette(), which is a really strange thing.

All of this goes to show that the default palette in ROOT is truly a mess. Thus, I’d be amazed if it is used for anything but offending our eyes. So why not change the default and save future users a little aggravation that spread over thousands of users becomes a lot of aggravation? In the rare case of an application expecting the old palette but needing to use a new version of ROOT one need add only a single line: gStyle->SetPalette(0). And as for changing the default TPad background, I could imagine even fewer unpleasant consequences for old code. Such changes are only cosmetic, with no change in the interfaces needed. There is no substantial issue of backwards compatibility.

For example, the default colors on the 2D histogram… are the palette of 16 colors computers used about 20 years ago!

Thanks for that comment. That’s amazing. I personally think the default style is okay for a computer screen. Terrible for presentation or document. For you developers it’s very difficult just to find the part about the plain style.

I think ROOTs great all in all, but I bet there are a few things like things this that seem very common but are very difficult to find in the docs or on the webpage.

Elliott