Dark mode is the most-requested feature I have refused to build. The reason is not aesthetic. It is structural.
A theme is not a colour palette. It is a parallel design system. Every shadow, every border, every state, every illustration, every chart, every icon needs a second specification. Every component needs to be tested in two configurations. Every visual decision needs to consider whether it works in both. The cost is not a one-off translation. It is a permanent doubling of the design surface.
For a team building a tool, this might be a reasonable trade. For a marketing operating system in which the user is generating content for their own brand, the trade is much worse.
The brand has only one face
Cleo is a creative tool. The user is producing emails, social posts, ad creatives, content pieces, brand guidelines. These artefacts will be seen by their customers in real-world contexts that I cannot control. The interface in which the user creates them should not change the colours they perceive while writing. Designing under a dark interface produces content that looks different when previewed against a light brand background. The mismatch is subtle and corrosive.
I picked one canon. A warm, paper-coloured surface. Slightly off-white backgrounds. Subdued accents that recede behind the user's own brand. The interface is restrained on purpose, because every pixel of attention it draws is a pixel taken from the work the user is doing.
The compounding cost
The decision not to build dark mode is one of dozens of similar decisions I have made. No customisable layouts. No alternative typography. No theme presets. No per-user accent colours. Each of these would be technically straightforward to add. Each would be modestly delightful to a small subset of users. Each would also fragment the design system into configurations that drift apart over time.
The cost compounds. With one canon, every component can be designed once, reviewed once, accessibility-tested once. With two canons, every component is designed twice, but worse than that, every interaction between components is tested twice. The combinatorial complexity of a design system grows faster than the number of themes.
Restraint is not minimalism
Cleo is sometimes called minimalist. It is not. Minimalism is the aesthetic preference for sparse interfaces. Restraint is a product discipline that says: every decision the user does not have to make is a decision they get to spend on their own work. These are different things.
The user has hundreds of decisions to make in a marketing platform. Which campaigns to run. Which audiences to target. What messages to send. What images to publish. What metrics to chase. Adding "which theme to use" to that list is not generosity. It is noise.
What I say to people who ask
I tell them that I considered it carefully and chose not to build it. That the warm surface is a deliberate choice, not an oversight. That the restraint is part of the product. Some of them are convinced and stay. Some of them are not and leave.
The ones who stay tell me, eventually, that the interface stops being something they notice. That is the test. A creative tool that disappears around the work is doing its job. A creative tool that has eleven theme variants is doing something else.
One canon. Carefully chosen. Held with discipline. The work in the centre.