colorstr() updates (#1909)

* W&B ImportError message fix

* colorstr() updates

* colorstr() updates

* colorstr() default to 'blue', 'bold'

* train: magenta

* train: blue

utils/general.py

@@ -118,7 +118,7 @@ def one_cycle(y1=0.0, y2=1.0, steps=100):
 
 def colorstr(*input):
     # Colors a string https://en.wikipedia.org/wiki/ANSI_escape_code, i.e.  colorstr('blue', 'hello world')
-    *prefix, string = input  # color arguments, string
+    *args, string = input if len(input) > 1 else ('blue', 'bold', input[0])  # color arguments, string
     colors = {'black': '\033[30m',  # basic colors
               'red': '\033[31m',
               'green': '\033[32m',
@@ -138,8 +138,7 @@ def colorstr(*input):
               'end': '\033[0m',  # misc
               'bold': '\033[1m',
               'underline': '\033[4m'}
-
-    return ''.join(colors[x] for x in prefix) + f'{string}' + colors['end']
+    return ''.join(colors[x] for x in args) + f'{string}' + colors['end']
 
 
 def labels_to_class_weights(labels, nc=80):