= Solution
For a canonical scalar field with positive kinetic energy, the <Friedmann equation> gives
$$
\dot H=-\frac{\dot\phi^2}{2M_{\rm Pl}^2}\leq0,
$$
so the <first Hubble slow-roll parameter> satisfies $\epsilon\geq0$. The tensor tilt is consequently
$$
n_T=-2\epsilon\leq0.
$$
A <blue primordial spectrum> of tensor modes cannot arise in standard canonical single-field slow-roll inflation; it requires changing assumptions, such as the matter content, kinetic structure, initial state, or gravitational dynamics.
The scalar tilt instead obeys
$$
n_s-1=-2\epsilon-\eta.
$$
It can be positive in a standard single-field model if $\eta<-2\epsilon$, meaning that $\epsilon$ decreases sufficiently rapidly with the number of e-folds. Equivalently, in potential slow-roll parameters the first-order condition is $2\eta_V>6\epsilon_V$. Thus a blue scalar spectrum is allowed by the framework, although it is not produced by every slowly rolling potential.
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