Dark color is not necessarily a sign of healthy compost/mulch. If it's dyed, the color is from chemicals, not humus. Not so healthy. Bagged mulch must tell you if it's dyed or not, so read the bag. If there's no mention of dye, you're good.
Now, because the (undyed) color doesn't affect the health of the product, using the city mulch is still a good idea, unless you want color for aesthetic purposes. So:
Bagged mulch if dyed will retain it's color much longer, and if undyed, most likely still a good bit longer, because bagged mulch is a much higher quality product than free city mulch. But remember, for soil health, it's not all about the color.
Yes, undyed bagged mulch will be at least as good for the soil as the city stuff. If dyed, you will be adding that much chemical dye to your soil.
Yes. Here are a few:
Bagged Mulch (undyed)
- (+) is much more consistent in texture and quality
- (+) is not going to contain as many possible contaminates like chipped black walnut limbs (a common issue with city mulch)
- (+) the color usually lasts fairly well, even when not dyed, because of proper 'cooking' methods and a more decomposed state
- (-) is much more expensive (obviously), which tends to limit the amount applied, which can (in some cases) decrease the rate at which your soil is improved
- (+) It's available in bulk, so you can supply your garden with as much as necessary without running up a big bill
- (+) Usually, the stuff is good enough for use in garden beds, some cities are more careful than others, though
- (-) The texture can be extremely uneven, and will break down irregularly, because of the many various species that went into it.
- (-) color fades fast, especially if the mulch hasn't decomposed for long. This is only aesthetic.