I represent SaaS companies in IP disputes and want to add some nuance to the trade dress discussion. Trade dress protection for software UI is genuinely difficult but not impossible, and the legal landscape is evolving.
In Apple v. Samsung, the courts recognized that product design (including digital interfaces) can be protected trade dress. However, the plaintiff must show: (1) the design is distinctive or has acquired secondary meaning, (2) the design is non-functional, and (3) there is a likelihood of confusion among consumers.
For SaaS specifically, the bigger opportunity may be under unfair competition law rather than pure trade dress. If your competitor copied not just the look but also your marketing copy, user flows, and brand positioning, you can argue they are attempting to pass off their product as yours or create false association. This is actionable under Section 43(a) of the Lanham Act without needing a registered trademark.
Practical steps that are often more effective than litigation: (1) file DMCA takedowns for any copied code or assets you can identify, (2) send a cease and desist specifically for the copied marketing copy, (3) document the timeline with archived screenshots using the Wayback Machine or a notarization service, (4) if they are using your actual CSS or JavaScript, that is straightforward copyright infringement and much easier to prove than trade dress.
The cold reality is that UI copying is rampant in SaaS and most companies choose to compete rather than litigate. But having documentation ready means you have the option if the copycat starts causing real market confusion.