I wouldn’t feel too sad about finding Dorico much better than Sibelius. The core of the Dorico development team are the London based Sibelius development team that Avid let go several years ago. Dorico gave the developers the chance to make a modern ‘clean sheet’ notation program without being constrained by existing user expectations or many years of technical debt. Dorico is not perfect; there are things Sibelius can do that Dorico still cannot, but Dorico is developing all the time and I look forward to the additional features Dorico 3 will have when it emerges.
Dorico adopts a modern design language and aesthetic that is similar to that found in Adobe Creative Cloud applications - dark flat background, user interface elements in shades of a very small colour palette and visual ornamentation (such as gradients and textures) kept to a few subdued examples. On my high-end calibrated monitor, I can see a slight gradient in the pale blue that surrounds the white music pages - it’s slightly lighter at the bottom, but it is a subtle effect. Dorico’s user interface is particularly reminiscent of Adobe Lightroom. As Fred says, the look of Dorico is similar in many ways to recent versions of Cubase, though there are differences in the icon design aesthetic and in the design of user interface elements such as button outlines. The different appearance of UI elements may well be in part because Dorico uses the Qt framework and Cubase does not.
Whilst it could be argued that the modern plain aesthetic makes the application less “pretty”, it is also potentially less distracting. I suspect that you are used to music looking a particular way on screen and are still adjusting to Dorico’s different look. I don’t think I have ever come across published sheet music printed on textured paper - normally it is on plain white to off white paper depending on the publisher. I remember the shock I experienced when I first moved to using Microsoft Office 2007, the first version with the Ribbon based user interface. It is many years since I used a non-Ribbon version of Office and expect I would find it very alien if I tried to use it again.
There is almost no customisation of the Dorico user interface appearance. In Dorico Pro 2, there is an option to choose a Light or Dark theme in Edit -> Preferences, and that is it! I suspect this option is available in Dorico Elements, but I don’t have an Elements licence on any of my computers.
I prefer the default dark theme, but the light theme is there for those that want it.