I. pallida 'Argentea Variegata' is slower to increase than I. p. 'Aurea Variegata' (aka: Zebra or just plain Variegata).
'Argentea Variegata' has silvery leaves with creamy white variegation.
'Aurea Variegata' has yellow variegation.
Both have the same blue flowers and a nice fragrance.
I've grown both for many, many years, and can't imagine a spring without the fresh foliage of either of these brightening up the garden.