I found ``RichText#add_run("text", :color => 'FF0000')``.
Thanks.
```ruby
if examples.include? :rich_text
p = Axlsx::Package.new
p.use_shared_strings = true
wb = p.workbook
wrap_text = wb.styles.add_style({:alignment => {:horizontal => :center, :vertical => :center, :wrap_text => true}} )
rt = Axlsx::RichText.new
rt.add_run('I\'m bold, ', :b => true, :color => 'FF0000')
rt.add_run('I\'m italic, ', :i => true)
rt.add_run('I\'m strike' + "\n", :strike => true)
rt.add_run('I\'m bold, italic and strike' + "\n", :b => true, :i => true, :strike => true)
rt.add_run('I\'m style-less :D')
wb.add_worksheet(:name => "RichText") do | sheet |
sheet.add_row [rt], :style => wrap_text
end
p.serialize 'rich_text.xlsx'
end
```