As a Roblox developer, it is currently hard to utilize the current UI in a way that can match the needs and themes of all possible types of games. As Roblox is growing, many devs are creating higher quality projects with an increasing demand for high quality, aesthetically sound UI. Because of the current UI system, there are only select design choices that can be translated through to Roblox without any tacky or unpolished artifacts. Even Roblox itself wants to expand to incorporate different themes and audiences, and for that Roblox needs to focus more on expanding its UI to allow for more creativity.
A great start to that expansion is to add blend modes to all UI objects (Image Labels, Textboxes, Frames, etc.). Blend modes (Multiply, screen, overlay, difference) for each GUI object would change the game on how UI designers create.
UI Examples
Dark Red, Blend mode: Normal
Red, Blend mode: Multiply
Lime Green, Blend mode: Difference
Navy Blue, Blend mode: Overlay
Sky Blue, Blend mode: Screen
Unity Blend Mode Plugin:
Blend Modes - YouTube
With blend modes, developers can be able to expand its current uses of UI to fit endless tones and themes, along with additional benefits with camera effects and UI particles. Allowing for different blend modes can bring the UI on Roblox to another level.