Warning about missing nREPL middleware descriptor when colorization is disabled

## Platform details

Platform (macOS, Linux, Windows): Windows 10
Platform version: Windows 10 Home, Version 1703, OS Build 15063.674
JRE/JDK version (`java -version`): JRE: "1.8.0_141"

## Boot details

Boot version (2.7.1): 2.7.1
`build.boot` present? (yes/no): yes
`~/.boot/profile` present? (yes/no): no
Task name? (if applicable): repl

### `build.boot` content (if applicable)

```clojure
;; build.boot content here
```

### `~/.boot/profile` content (if applicable)

```clojure
(task-options!
pom {:project 'ignition-project
:version "1.0"
:description "Fix me"
:license {"EPL" "http://www.eclipse.org/legal/epl-v10.html"}})
```

## Description
I get the following error when I run "boot repl"
[WARNING] No nREPL middleware descriptor in metadata of boot.repl$disable_exception_colors@4c415a68, see clojure.tools.middleware/set-descriptor!
nREPL server started on port 55825 on host 127.0.0.1 - nrepl://127.0.0.1:55825
REPL-y 0.3.7, nREPL 0.2.12
Clojure 1.8.0
Java HotSpot(TM) 64-Bit Server VM 1.8.0_60-b27

Why is this happening? Does it cause any problems? Is there a way to fix it? Thanks for your help.

Start by reproducing the warning with the reported `boot repl` task and inspect the `boot.repl$disable_exception_colors` entry named in the message. Trace where that function is registered with nREPL, then check whether the warning is expected when colorization is disabled. Done means the cause and user-visible impact are established and the warning is corrected or clearly documented.

Written by the indexing model from the issue text.