The items using item/generated are darker than the actual textures, even if they are not translucent. You can see this in the attached image (do not pay attention to what they are, these are just for testing). The purple in the first item is #C00069 instead of #F800F8, the latter of which is the intended color.

EDIT: Possibly dependent on what graphics card/integrated graphics is being used, as I have tested on both snapshots (20w51a and 21w15a) using Intel HD Graphics 4600 (i7-4790K iGPU), and the color in both snapshots is #F500F5. This is still a bit darker but to a lesser extent than the result above, which is using Intel HD Graphics 4400 (i3-4160 iGPU). I attached a test pack that replaces the stone pickaxe with the same texture as the one in the image.

EDIT2: Using AMD Radeon HD 6750 also gives the same result as using Intel HD Graphics 4600.

EDIT3: Using NVIDIA GeForce GTX 960 gives the same result as both of the above.