Themes decide how much of the data a reader can actually see. In ATAS a theme is a palette plus a set of mapping rules; rendering options decide how those rules are applied and how much work the renderer is asked to do per frame.
01 Palette structure
A palette is organised in roles rather than in colours. Background, grid, text, up-move, down-move, cluster text, event highlight and selection each hold one value. Because the roles are separate, changing the accent does not disturb cluster text contrast, and a theme can be adjusted for a projector without disturbing the numeric layer.
| Role | Default example | High contrast |
|---|---|---|
| Background | #F7F3EC | #FFFFFF |
| Cluster text | #1E1B18 | #000000 |
| Up move | #3E6B4F | #1F5C36 |
| Down move | #B3123A | #8E0E2E |
| Event highlight | #5A4E7C | #2E2350 |
The table above is illustrative: the practical rule is that cluster text must remain readable against every band it can be drawn on, including the darkest band of the size scale.
02 Cluster colour mapping
Footprint colouring is a mapping from value to band. Three mapping styles are common: fixed thresholds, percentile-based bands within the visible window, and a continuous gradient. Fixed thresholds produce comparable colours across sessions; percentile bands produce a picture in which every bar contains both extremes; gradients are visually smooth but hard to read quantitatively.
- Fixed — one set of thresholds for the whole instrument, stable over time.
- Windowed — thresholds recomputed from the visible bars, sensitive to scrolling.
- Gradient — continuous fill, best for shape recognition rather than measurement.
Whatever the style, the same style must be stated when a chart is shared; otherwise two readers will disagree about which band a row belongs to.
03 Axis, grid and label styling
Axes consume a surprising share of a chart's readability budget. A price axis with too many labels competes with footprint text; a time axis with minute resolution on a tick-count chart produces labels that do not correspond to bar boundaries. Reducing axis density and aligning labels to bar closes is usually a larger gain than any colour change.
- Set label density by pixel distance, not by fixed intervals.
- Align time labels to bar boundaries when the bar rule is event-based.
- Keep the grid at lower contrast than cluster text, always.
04 Rendering options and draw budget
Rendering options trade detail for frame time: text smoothing, shadow effects, animated highlights and the number of simultaneously drawn indicator instances. The practical budget is a frame rate that stays comfortable while scrolling; when it does not, the first things to reduce are animated effects and the number of price rows drawn per bar.
| Lever | Visual gain | Cost |
|---|---|---|
| Text smoothing | Cleaner numbers at small sizes | Low, per glyph |
| Row shadows | Depth separation | Medium, per row |
| Animated highlights | Event visibility | High, per frame |
| Extra instances | More context | High, per bar per instance |
The hardware side of the same question, including how recorded data volume interacts with rendering cost, is discussed on the performance and hardware notes page.
05 Themes, contrast and accessibility
Two colours that are distinguishable on one display may be identical on another. Contrast should be checked in terms of relative luminance rather than by eye, and the numbers inside a footprint row need a contrast ratio that survives compression and screenshotting. Readers using the site itself should find the same discipline applied here: see the accessibility statement for the conformance notes on this reference.
The instance-level options that a theme cannot set — inputs and aggregation overrides — are listed in the indicator module reference.