Hi Michal,
Thank you for your interest in Syncfusion products.
You can use collection of ConditionalFormats by using IConditionalFormats interface. If you want to change the color from red to green with the numbers you can set the condition like below:
[C#]
sheet.Range["E1:E20"].CellStyle.ColorIndex = ExcelKnownColors.Red;
//Applying conditional formatting to "E1 to E20" for format type as CellValue( Between)
IConditionalFormats condition = sheet.Range["E1:E20"].ConditionalFormats;
IConditionalFormat condition1 = condition.AddCondition();
//Set the condition
condition1.FirstFormula = "10";
condition1.SecondFormula = "20";
//Setting format properties.
condition1.Operator = ExcelComparisonOperator.Between;
condition1.FormatType = ExcelCFType.CellValue;
condition1.BackColorRGB = Color.FromArgb(0, 100,0);
Here is the sample for your reference:
http://www.syncfusion.com/development/uploads/XlsIO_ConditionalFormatting_be69897b.zipAlso please refer our shipped browser sample that demonstrates how conditional formatting can be applied with Essential XlsIO.
\Syncfusion\EssentialStudio\6.3.0.30\Windows\XlsIO.Windows\Samples\2.0\Formatting\ConditionalFormatting\CS
Please try this and let me know if this helps.
Regards,
G.Yavana