Colour film usually responds less well to over- or under-exposure.
If you under-expose, you could lose satuation which results in a drab look. You may also get colour shifts if you need to develop it for longer.
A small amount of over-exposure may increase saturation but if you go too far it won't look good either.
Generally, I shoot most films at box speed, especially colour. It is best for predictability and consistency of the results.
Do experiment, by all means, but bear in mind that C41 development is prone to slight variations, even if you use a pro lab. If you develop it yourself, you may get very varying results between the batches.
If you are going to shoot under varying light, it's best to bring slow, normal and fast film, and to use a good lens with a large aperture span.