JSFiddle - React, Tailwind, and code Playground

HTML

<span>header</span>
		
		<br />
	
		<div class="logo">
			weterteyrtutyu<span class="rainbow_text" >sergey kalinin 123</span>wqeqweqwqrvdg
		</div>
		
		<br />
		
		<span class="rainbow_text" >qwerty asdf zxzx</span>
		
		<br />
		
		<span>footer</span>
		
		<br />
		
		<span class="rainbow_text" >qzx</span>

JavaScript

function KalininRainbowText(options){
	// ------------------------------------------------------------------------------------------ properties ---------	
	var	self = options.element,
		colorArray = options.colorArray || new Array('#974bff', '#ec11a1', 'navy', 'orange', '#ecb111', 'magenta', '#055d12', '#4bb1ff'),
		colorArrayLength  = options.colorArray.length,
		text = self.innerHTML,
		textLength = text.length;
		
	init();

	// ------------------------------------------------------------------------------------------ methods ------------	
	function init(){
		self.innerHTML =colorize(textLength, text);
	}	

	function colorize(textLength, text){
		var	newText = '',
			colorLetter,
			i;
			
		for(i = 0; i < textLength; i++){			
			newText += '<span style="color: ' + (options.colorArray[Math.floor(Math.random() * (colorArrayLength))]) + '">' + text.substr(i, 1) + '</span>';
		}	

		return newText;		
	}	

	// ------------------------------------------------------------------------------------------ handlers -----------		
	
	// ------------------------------------------------------------------------------------------ events -------------			
}


new KalininRainbowText({
				element: document.getElementsByClassName ('rainbow_text')[0], 
				colorArray: new Array('red', 'lime', 'blue', 'navy', 'green', 'magenta', '#883f46', '#4bb1ff')			
			});	

			new KalininRainbowText({
				element: document.getElementsByClassName ('rainbow_text')[1], 
				colorArray: new Array('red', 'lime', 'blue', 'navy', 'green', 'magenta', '#883f46', '#4bb1ff')			
			});	

			new KalininRainbowText({
				element: document.getElementsByClassName ('rainbow_text')[2], 
				colorArray: new Array('red', 'lime', 'blue', 'navy', 'green', 'magenta', '#883f46', '#4bb1ff')			
			});