When it comes to the convenience of carrying a single pen rather then four pens, the solution is a four in one colour pen

•  Each pen includes a retractable black, blue, red and green ink colour
•  Ink pen is tamperproof, waterproof and fadeproof
•  Regulated ink flow to avoid scratching and blobbing
•  Ink Colours include black, blue, red and green all in one pen
•  Made in China