Part of my priority when creating new tea blends has been to deliver choices, with different cups of tea to suit different moods or different times of the day. For me, that translated into relaxing blends like Lull an ideal blend for when I want to calm down, but without the soporific effects of something like chamomile (like taking a quick breather from writing for example). Blends like Carrot Cake, on the other hand, suit me when I want to feel cosy and homely, while I might take Mint Choc Chip should I wish to inspire a sense of refreshment and rejuvenation in me (what else would you expect from peppermint?). There is an important role for caffeine in all of this.
Caffeine in and of itself is a clear and odourless stimulant; a tame, but naturally occurring psychoactive drug found in beans (like coffee), leaves (such as tea) and even in nuts and fruit. When it's dunked in hot water, such as when brewing a hot drink, it also becomes bitter, which is what makes brewing a green tea so troublesome and what turns some people off the taste of coffee altogether (but only if they've got the right genes). These qualities are what make caffeine such an important fixture in partnering a drink with a feeling or a mood, or even music. Part of why Lull works to calm but sharpen the mind is that it begins with green tea as a base ingredient. In not too science-y terms, this means that although there is a healthy dose of caffeine in the leaf it's effects are inhibited by L-Theanine; an amino acid that's also present in the leaf, which serves to gently soothe and calm the nervous system.
Surely, these effects do seem at odds with one another, suggesting that they should simply cancel one another out, but this isn't quite the case. Rather, It provides a more gentle and balanced boost. To understand this more clearly we could contrast it against another popular purveyor of stimulation; coffee. Coffee is a good example of something very high in caffeine, it can have roughly three times as much as a green tea, giving it a hugely energising role in the body. However, the intensity of coffee's caffeine high is often followed by a precipitous crash into some kind of bean induced semi-coma, which is not true of green tea, a more subtle affair all around. The back of the book here is that green tea offers a slower, more gradual uplifting sensation compared to coffee. It is a little like comparing the effect of a leisurely jog on your heart with the same effect after being fired out of a cannon. Notably different.
Unlike coffee and the various progeny of Camellia Sinensis (any white, green, black or oolong teas) Rooibos (meaning red-bush) is another type of leaf, that is naturally caffeine-free. I often use the leaves in many of my blends when I want something similar in texture to the everyday black tea blend but without the prolonged stimulating effects (caffeine can take until the end of the day to exit your system, even if you have it first thing in the morning) making it ideal to have in the evening before bed. So, should I want to feel quite cosy after a long day at work or when the weather is thundering there's nothing better than something with a red tea base, something like Rhubarb and Custard or Carrot Cake. It won't negatively impact on my sleep, where a black might, but it will still offer that satiated feeling that I get from drinking a thick, rich tea. In other words, you can have your (liquid) cake and eat it.
It would be silly of me to finish up this without saying anything about black tea. Black tea is more comparable to green tea than it is to coffee. Most obviously, it comes from the same bush. It is also likely to have somewhere around double the caffeine found in a green and around half that you'd expect from coffee making it ideal (and rather common) for the morning or as a more committed pick-me-up (but still, with much less of crash) later on in the day. There are good reasons for this that vary from the region the tea is from, the part of the leaf used, the way the tea is processed after being picked and a few other things, but there's little control to be had when you've already got the kettle on at home. In Mint Choc Chip I simply use less of it, but you can reduce the final amount of caffeine achieved simply by brewing the tea for a shorter amount of time or by steeping it in cooler water. These two factors alone can have quite a profound impact on the caffeine levels in the tea (it's completely possible for the caffeine levels in a white tea to exceed those in a black tea simply by playing around with temperature and time, quite contrary to popular opinions).
Now for the short answer. Is there caffeine in tea? The answer is yes, simply because the word tea refers to a specific kind of leaf from a specific species of evergreen bush. Technically, a tea with a rooibos base is a misnomer; it isn't a tea at all, it's a herbal infusion and the same can be said of any other herbal blend (like Little Picture). It is only a tea if it is brewed from the leaves of Camellia Sinensis.
Practically speaking, if you want a zero caffeine blend that seems just like an 'ordinary' tea then try a rooibos based blend. But, if you want caffeine then try something either white, green, black or oolong.