http://www.wizards.com/Magic/Magazine/Article.aspx?x=judge/article/20071126aThis will give you the specifics of how continuous effects interact with each other. It is updated for M10 rules.
Essentially, whenever continuous effects interact there is a layer system. Continuous effects are applied in order of their layers, going 1, 2, 3, etc.
Layer 1 - Copy Effects
Layer 2 - Control Changing Effects
Layer 3 - Text Changing Effects (note 612.3 - Effects that add or remove abilities don't change the text of the objects they affect)
Layer 4 - Type Changing Effects
Layer 5 - Color Changing Effects
Layer 6 - Ability Adding and Ability Removing Effects
Layer 7 - Power/Toughness (with various sub-layers)
Servant's color-changing effect applies in layer 5. Humility's ability removing effect applies in layer 6. Thus, Servant will still have the color-changing effect even with Humility in play because the Servant's ability is in an earlier layer.
The change in M10 rules is in the specific layers. Previously, color changing effects and ability adding/removing effects were both applied in layer 5, which caused Humility to overwrite Servant. With the restructure of M10 rules, their effects are applied in different layers.
