BUG: Tweening converts some text labels to hex codes, fails when combined with other text

[katrinabrock]

Issue trigger

Create an animation with an impacted text string as the label, for example 0 pi.

Expected behavior

This labels shows up both in main plots and transitional frames.

Actual behavior

Either the plot totally fails to render, with the error Error: The labelcolumn differs in type between the two inputs or transitional frames are labeled with #FFFFFF00.

MRE

anim_save(
  'example.gif',
  ggplot(aes(x=x,y=y,label=label), data = data.frame(
    label = '0 pi',
    x = 1:4,
    y = 1:4,
    frame = 1:4
  )) + geom_text() + transition_states(frame),
  nframes = 31,
  fps = 5
)

Results in:

anim_save(
  'example.gif',
  ggplot(aes(x=x,y=y,label=label), data = data.frame(
    label = c('0 pi', '0 pi', 'other', 'labels'),
    x = 1:4,
    y = 1:4,
    frame = 1:4
  )) + geom_text() + transition_states(frame),
  nframes = 31,
  fps = 5
)

Errors out with

Error : The labelcolumn differs in type between the two inputs

Likely from here: https://github.com/thomasp85/tweenr/blob/main/R/tween_state.R#L157

Exploring a little, the mis-match types are colour vs character, but not sure how this came to be.