1)But I want my creature to have blue "blood". Can I do this without defining a custom blood material?
It is common to use SET_TL_GROUP and TL_COLOR_MODIFIER to change color. For example:
2) And if this does work, is [TLCM_NOUN:blood:SINGULAR] needed to make it display properly?
Those tokens are used for descriptor modifiers. They do nothing to the actual material (hair, for example, is always GRAY so long as it's called from the basic template, but it's described as being different colours).
What you want to do is select the material and change the actual colour:
[SELECT_MATERIAL:ICHOR]
[STATE_COLOR:ALL_SOLID:BLUE]
[STATE_COLOR:LIQUID:BLUE]
[STATE_COLOR:GAS:BLUE]
3) I want the stinger of my custom creature to have a very good chance of penetrating even steel armor in order to inflict a syndrome. I suppose one possibility would be to modify the ATTACK_CONTACT_PERC and/or ATTACK_PENETRATION_PERC.
Not without forcing it to behave weirdly. By raising the contact perc you're turning that stinger into a blade. An alternative which doesn't show up in the vanilla game is ATTACK_VELOCITY_MODIFIER. Use that in the same place as the contact/penetration tags and set it to something high (several hundred).
Would I define a custom material for the stinger like this?:
[BODY_DETAIL_PLAN:CHITIN_MATERIALS]
[USE_MATERIAL_TEMPLATE:TAIL_STINGER:METAL_TEMPLATE]
Or would that be [USE_MATERIAL_TEMPLATE:STINGER:METAL_TEMPLATE] ?
When you use USE_MATERIAL_TEMPLATE or USE_TISSUE_TEMPLATE, you're defining a material or template. It's just a shortcut to typing the entire thing out (see: bronze colossus entry). In order to actually use it, you need to use TISSUE_LAYER.
In the case of inorganic materials it's easier just to define things sans template:
...
[TISSUE:STINGERTIP]
[TISSUE_NAME:stinger-tip:stinger-tips]
[TISSUE_MATERIAL:INORGANIC:STEEL]
[RELATIVE_THICKNESS:1]
[CONNECTS]
[TISSUE_SHAPE:LAYER]
[TISSUE_LAYER:BY_CATEGORY:STINGER:STINGERTIP]
...
(Make sure this is after the body detail plans. The tissue might need the MUSCULAR tag or something as well, I forget.)
The material will still be referred to as "steel" in combat at times. The only way of getting around that is to define an entirely new material within the creature entry, based on the metal template, with the properties of steel and a different name. It's necessary to do this as you can't modify materials which aren't part of the actual creature entry (in the form of templates or otherwise).