<?php

$color = new Colors('FF0000', 'FFFF00', 100);

var_dump($color->step(10)); // hex
var_dump($color->step_rgb(10)); // rgb


class Colors {

    function __construct ($start, $end, $steps){

        // convert hex into rgb arrays
        $this->start = $this->hex_rgb($start);
        $this->end = $this->hex_rgb($end);

        // calculate the step size required the two rgb arrays
        $this->num_steps = $steps;
        $this->step = $this->rgb_step($this->start, $this->end, $this->num_steps);

    }


    // returns the hex color
    public function step ($num){

        if ($num > $this->num_steps) $num = $this->num_steps;
        return  str_pad(dechex($this->start['red']+($this->step['red']*$num)),2,'0',STR_PAD_LEFT).
                str_pad(dechex($this->start['green']+($this->step['green']*$num)),2,'0',STR_PAD_LEFT).
                str_pad(dechex($this->start['blue']+($this->step['blue']*$num)),2,'0',STR_PAD_LEFT);
    }


    public function step_rgb ($num){

        if ($num > $this->num_steps) $num = $this->num_steps;
        return  intval($this->start['red']+($this->step['red']*$num)).','.
                intval($this->start['green']+($this->step['green']*$num)).','.
                intval($this->start['blue']+($this->step['blue']*$num));
    }


    private function hex_rgb($hex){

        return ['red' => hexdec(substr($hex,0,2)),
                'green' => hexdec(substr($hex,2,2)),
                'blue' => hexdec(substr($hex,4,2))];

    }


    private function rgb_step($start, $end, $steps){

        return ['red' => ($end['red']-$start['red'])/$steps,
                'green' => ($end['green']-$start['green'])/$steps,
                'blue' => ($end['blue']-$start['blue'])/$steps];

    }
}