A clear plastic bottle can work, but light is usually less of a problem than air. The key is to store the developer tightly sealed with as little air space as possible.

Best practice from the community advice:

• Keep the bottle nearly full.
• Store it in a dark place if the container is transparent.
• Glass bottles are preferred because they’re less permeable and less likely to contaminate the solution.
• Brown or green glass filled to the top is ideal.
• If the bottle is no longer full, you can use clean marbles to raise the liquid level and reduce air space.
• A squeezable accordion-style chemical bottle is also a good option because you can compress it to remove most of the air.

So: your clear plastic bottle is not automatically harmful, especially if it’s kept in the dark, but minimizing contact with air is more important for preserving the developer.