Chart series Fill with Type "solid" not applying custom colors

[ohauer]

Chart series Fill with Type "solid" not applying custom colors

Description

Chart series with Fill{Type: "solid"} do not apply custom colors. Charts always use Excel's default theme colors instead of the specified RGB colors.

Environment

• excelize version: v2.10.0
• Go version: 1.25.7
• OS: Linux

Expected Behavior

When creating a chart with custom fill colors using Type: "solid":

Fill: excelize.Fill{Type: "solid", Color: []string{"FFCCCB"}}

The chart series should display in the specified color (light red #FFCCCB).

Actual Behavior

The chart ignores the custom color and uses Excel's default theme colors (blue shades).

Minimal Reproduction

package main

import "github.com/xuri/excelize/v2"

func main() {
    f := excelize.NewFile()
    defer f.Close()

    // Add test data
    f.SetCellValue("Sheet1", "A1", "Category")
    f.SetCellValue("Sheet1", "A2", 100)

    varyColors := false
    
    // Try to create red bar
    f.AddChart("Sheet1", "C1", &excelize.Chart{
        Type:       excelize.Bar,
        VaryColors: &varyColors,
        Series: []excelize.ChartSeries{
            {
                Name:       "Test",
                Categories: "Sheet1!$A$1:$A$1",
                Values:     "Sheet1!$A$2:$A$2",
                Fill:       excelize.Fill{Type: "solid", Color: []string{"FFCCCB"}}, // Should be red
            },
        },
    })

    f.SaveAs("test.xlsx")
}

Result: Bar appears in default blue instead of red.

Root Cause

File: drawing.go, function drawShapeFill() (line ~840)

The function only processes Fill colors when Type == "pattern" && Pattern == 1:

func (f *File) drawShapeFill(fill Fill, spPr *cSpPr) *cSpPr {
    if fill.Type == "pattern" && fill.Pattern == 1 {  // <-- Only checks pattern
        // Apply custom color
    }
    return spPr
}

This means Type: "solid" is completely ignored.

Workaround

Use Type: "pattern" with Pattern: 1 instead:

Fill: excelize.Fill{Type: "pattern", Pattern: 1, Color: []string{"FFCCCB"}}

Proposed Fix

Change the condition to also accept Type: "solid":

if fill.Type == "solid" || (fill.Type == "pattern" && fill.Pattern == 1) {

Impact

• Affected: All chart types (bar, line, pie, scatter, etc.)
• Also affects: DataPoint colors, markers, plot area fills, up/down bars
• Severity: Medium - workaround exists but not intuitive
• Breaking change: None - only adds support for previously ignored syntax

Pull Request

I have a fix ready with tests. Branch: fix/chart-fill-solid-type #2260

Tested with:

• ✅ Bar charts with 5 custom colored series
• ✅ Pie charts with DataPoint colors
• ✅ All colors render correctly

[xuri]

Thanks for your issue. As the documentation of NewStyle function says:

The 'Fill.Type' use to set fill type, supported types are 'gradient' or 'pattern'.

The solid is not a valid fill type, please set solid fill style for chart series like this:

+Fill:       excelize.Fill{Type: "pattern", Color: []string{"FFCCCB"}, Pattern: 1},
-Fill:       excelize.Fill{Type: "solid", Color: []string{"FFCCCB"}}, // Should be red

Also reference 3rd example in SetCellStyle function.