A basic script to help calculate the average color between 2 supplied RGB values

AvgRGBColor.js

// get the average color of two rgb colors.
function avgcolor(color1,color2){
	/// declare vars
  let   avg,
        hex16,ch16,
        hex1,hex2,
        r,g,b,
        res;

  // get average of channel hex
  avg  = function(a,b){ 
    return (a+b)/2; 
  }
  
  // convert to 16 bit hex
  hex16  = function(c){ 
    return parseInt((''+c).replace('#',''),16); // ie. 2923191 or 16099355
  }
  
	// hex component conversion
  ch16  = function(c){ 
		var t = (c>>0).toString(16);
        return t.length == 2 ? t : '0' + t; // ensure there are at least 2 digit
  }
  
  /// container for hex values
  hex1 = hex16(color1); // hex value 1
  hex2 = hex16(color2); // hex value 2
  
  // return Rgb component of hex value
  r = function(hex){ 
    return hex >> 16 & 0xFF;
  }
  
  // return rGb component of hex value
  g = function(hex){ 
    return hex >> 8 & 0xFF;
  }
  
  // return rgB component of hex value
  b = function(hex){ 
    return hex & 0xFF;
  }
  
  // compile back to rgb
  res  = '#' + ch16(avg(r(hex1),r(hex2))) + ch16(avg(g(hex1),g(hex2))) + ch16(avg(b(hex1),b(hex2)));

  return res;  // return resulting rgb average
}

console.log(avgcolor('#2c9ab7','#f5a81b')); // "#90a169"