This hubl macro will determine text color based on a set background color. This macro is based off of this sass color function by John W Long https://gist.github.com/jlong/f06f5843104ee10006fe which is based off of this article http://www.nbdtech.com/Blog/archive/2008/04/27/Calculating-the-Perceived-Brightness-of-a-Color.aspx

hubl_brightness_macro.css

{#  This macro is based off of this sass color function by John W Long 
 #  https://gist.github.com/jlong/f06f5843104ee10006fe
 #  which gets its brightness math from this article:
 #  http://www.nbdtech.com/Blog/archive/2008/04/27/Calculating-the-Perceived-Brightness-of-a-Color.aspx
 #  Thanks to Matt Coley (https://github.com/mattcoley) and the HubSpot Team
 #  for introducing the root filter which makes this macro possible.
 #}

{% macro find_text_color(bg_color) %}
  {%- set rgb_array = bg_color|convert_rgb|split(',') -%}
  {%- set r = rgb_array[0]  -%}
  {%- set g = rgb_array[1]  -%}
  {%- set b = rgb_array[2]  -%}
  {%- set red_changer = 241 -%}
  {%- set green_changer = 691 -%}
  {%- set blue_changer = 68 -%}
  {%- set brightness_divisor = red_changer + green_changer + blue_changer -%}
  {%- set light_text = '#f6f6f6' -%}
  {%- set dark_text = '#222222' -%}
  {%- set to_calculate = (((r * r * red_changer) + (g * g * green_changer) + (b * b * blue_changer)) / brightness_divisor )|root -%}
  {%- set brightness =  100 * to_calculate / 255 -%}
  {%- if brightness < 65 -%}{{ light_text }}{%- else -%}{{ dark_text }}{%- endif -%}
{% endmacro %}

{#  example use 
 #  {{ find_text_color('#073B3A') }}
 #  will output #f6f6f6 
 #} 

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