<form method= "POST" action="12laba3.php">
<input name="mycolor[]" type="checkbox" value="red"> Р
<input name="mycolor[]" type="checkbox" value="blue"> З
<input name="mycolor[]" type="checkbox" value="black"> К
<input name="mycolor[]" type="checkbox" value="white"> М
<input name="mycolor[]" type="checkbox" value="green"> Б
<br>
<input type="submit" value="Ok">
</form>