The kelp has a dark color

Java Edition

Bedrock Edition

Are you sure this is the kelp itself? It may just be a difference in brightness (MCPE-84513) and the water fog color (MCPE-125147) that makes the kelp look different.

here the problem is with the Kelp plant looks dark green compared to Java Edition. Postscript ignores the color of the underwater background in Bedrock I did that the error only affects the Kelp plant that I cannot modify

yes, I created a white image as its texture then only to find that was in green tinting slightly in game world, and this is the reason why we see it darker

here is the image in bedrock edition but without the color of the water changed and you will see that the Kelp has a dark color

I have confirmed this by custom resource pack, kelp is greenly tinted by hardcode, although the texture images are green themselves.

I remember the seagrass was also tinted before but the bug was fixed, however nobody noticed the bug is also in kelp till this page... (MCPE-34795)

I can see the difference now; it is very clear if you break one kelp plant in front of another because the broken kelp particles are not the same color as the kelp block.