But if you look at the examples of GXT 3.0.1 and GXT 2.3.0, the Combobox seems different.
You can verify this in the second picture.
I have looked into the trigger-sprites of GXT 2.3.0. In the resources, if you go in the path "resources\images\default\form", you can see the sprites of every trigger. Everyone has the same look and seems to descended from trigger-tpl.gif. But the first state of trigger.gif is different, without the color change. This ist the one for the combobox. So the trigger always looks different.
Interesting to note, and probably not deliberate, but a bug? If you require GXT to look identical to Ext JS, you can create an appearance that will make these details the same (or custom css in gxt 2).
I can file it, but this is a) behaving correctly and b) internally consistent, so I'm not sure how high of priority this will be, especially considering that this has been consistently different for quite a while (i.e. we would be changing the look for any app that has used GXT 2 or 3 up until now, and possibly 1, though I don't have that running locally atm).
Our target release for 3.1.0 is two months after the beta, which puts it right now, and we're freezing code and going through vigorous testing, so we're a few weeks too late to reconsider something like this, especially after a year of no follow up from any user.
GXT 2 is being used as the benchmark for GXT 3 look and feel, except for Neptune, where we are starting with Ext JS's version, and making allowances for the fact that the theme is being applied to a totally different codebase, and as a requirement of the project must be customizable without writing code, only config. The GXT 3.1 final theme builder will include basic functionality to allow developers to replace images with either compiled images or SVG files that should have theme properties applied to them, so this customization should be available to you in any new theme going forward.