How to Dynamically Color Syncfusion Blazor Chart Data Labels Based on Background for Readability
I have a scenario where the data label for a point sometimes appears on a white background (for example, when the line value is outside the range column), and the default label color is white (because most of the time it falls inside a dark blue background box so white is the most readable color for it). This makes the label invisible or very hard to read (white text on white background).
Example:
For "Wed 8/27/2025 PM", the "Prime Model" value is 15000, which falls outside the colored range box, so the label appears on the chart's white background. Since the label font is also white, it is not visible.
Minimal Repro:
https://blazorplayground.syncfusion.com/hXhyjlLhsABCnFTj
Requirement:
- I want to dynamically set the label color based on the background it appears on, so that the label is always readable (e.g., use black text on a white background, white text on a dark background, etc.).
- I know how to compute a contrasting text color if I know the background color. For example, I can use this method:
// Pass background hexColor to get appropriate text color
public static string GetContrastTextColor(string? hexColor)
{
if (string.IsNullOrWhiteSpace(hexColor))
return "black";
if (!hexColor.StartsWith("#"))
{
return hexColor.ToLower() switch
{
"white" => "black",
"black" => "white",
"red" => "white",
"blue" => "white",
"yellow" => "black",
_ => "black"
};
}
hexColor = hexColor.TrimStart('#');
if (hexColor.Length != 6) return "black";
int r = Convert.ToInt32(hexColor.Substring(0, 2), 16);
int g = Convert.ToInt32(hexColor.Substring(2, 2), 16);
int b = Convert.ToInt32(hexColor.Substring(4, 2), 16);
double luminance = (0.299 * r + 0.587 * g + 0.114 * b) / 255;
return luminance > 0.6 ? "black" : "white";
}
- However, I do not know how to get the actual background color for each label at runtime, especially when the label is rendered outside the range column (on the chart background).
- I have many series and dynamic data, so I need a solution that works for any number of series and does not require hardcoding colors for each point.
Questions:
1. How can I determine the background color behind each data label (especially for line series points that may be outside the range column)?
2. Is there a built-in way in Syncfusion Blazor Charts to automatically set a readable label color based on the background, or a recommended approach for this scenario?
3. If not, is there an event or callback where I can dynamically set the label color for each point based on its position/background?
Request:
Please provide guidance or an example on how to achieve dynamic, readable label coloring based on the background in Syncfusion Blazor Charts.
Thank you!
Hi Ashish,
You can check the background color of chart using ChartArea Background color. For your reference, we have attached the modified sample and screenshot.
|
<Syncfusion.Blazor.Charts.SfChart> <Syncfusion.Blazor.Charts.ChartArea Background="@bgColor"></Syncfusion.Blazor.Charts.ChartArea> </Syncfusion.Blazor.Charts.SfChart> @code { public string bgColor = "white"; public void LabelRenderEvt(Syncfusion.Blazor.Charts.TextRenderEventArgs args) { if (args.Series.Type == Syncfusion.Blazor.Charts.ChartSeriesType.Line) { if ((bgColor == "white" || bgColor == "transparent") && args.Point.Index == 6) { args.Font.Color = "black"; } else { args.Font.Color = "white"; } } } } |
Sample : https://blazorplayground.syncfusion.com/hNByDFVhqOrbYvXN
UG :
https://blazor.syncfusion.com/documentation/chart/chart-appearance#chart-area-customization
https://blazor.syncfusion.com/documentation/chart/events#ondatalabelrender
Please let us know if you have any concerns.
Regards,
Durga Gopalakrishnan.
Hi Durga,
Thank you for the response, but it looks like you misunderstood the question.
I didn't expect you to hardcode args.Point.Index because we can't know where the line label will fall into a white background.
I have added comments about this on your code:
https://blazorplayground.syncfusion.com/VDLeXlhLIrKJPbuP
And when you remove that hardcoding, it doesn't work correctly.
I only need black font color for line label for Thu, 08/28/2025 PM because that label falls on white background, but it gives black font to every label in the line chart.
In addition to detecting background color to come up with label color (the most safe and desirable approach), maybe also explore this approach:
Check the label value of the line chart and if it falls outside the high and low values of the range box, color it differently.
---
Also how to smartly place the label if it's close to getting outside the box?
Instead of putting that 17,351 on the top of line chart marker, it could have been placed on the bottom, and it'd have looked much better:
I tried this but that didn't make it any better:
Keep in mind I can't put LabelPosition.Bottom because I'll face similar issue there as well, so I need a robust solution for this.
Please help making these labels easy to read.
